10-K 1 aonplc201510-k.htm 10-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

Commission file number: 1-7933

Aon plc

(Exact name of registrant as specified in its charter)

Securities registered pursuant to Section 12(g) of the Act: NONE

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. YES ý NO o

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Exchange Act. YES o NO ý

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. YES ý NO o

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). YES ý NO o

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant's knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K. o

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of "large accelerated filer," "accelerated filer," and "smaller reporting company" in Rule 12b-2 of the Exchange Act.

(Do not check if a smaller reporting company.)

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). YES o NO ý

As of June 30, 2015, the aggregate market value of the registrant's Class A Ordinary Shares held by non-affiliates of the registrant was $27,889,141,346 based on the closing sales price as reported on the New York Stock Exchange — Composite Transaction Listing.

Number of Class A Ordinary Shares of Aon plc, $0.01 nominal value, outstanding as of February 5, 2016: 270,081,701.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of Aon plc's Proxy Statement for the 2016 Annual General Meeting of Shareholders to be held on June 24, 2016 are incorporated by reference in this Form 10-K in response to Part III, Items 10, 11, 12, 13 and 14.

PART I

OVERVIEW

Aon plc's strategy is to be the preeminent professional service firm in the world, focused on the topics of risk and people. Aon plc (which may be referred to as "Aon," "the Company," "we," "us," or "our") is the leading global provider of risk management services, insurance and reinsurance brokerage, and human resource consulting and outsourcing, delivering distinctive client value via innovative and effective risk management and workforce productivity solutions. Our predecessor, Aon Corporation, was incorporated in 1979 under the laws of Delaware. In 2012, we reincorporated in the U.K. and moved our corporate headquarters to London. As a result of this reorganization of our corporate structure, Aon plc became the publicly-held parent company of the Aon group. We sometimes refer to this transaction herein as the Redomestication.

We have approximately 69,000 employees and conduct our operations through various subsidiaries in more than 120 countries and sovereignties.

We serve clients through the following reportable segments:

Our clients are globally diversified and include all segments of the economy (individuals through personal lines, mid-market companies and large global companies) and almost every industry in the economy in over 120 countries and sovereignties globally. This diversification of our customer base provides stability in different economic scenarios that may affect specific industries, customer segments or geographies.

We have continued to focus our portfolio on higher margin, capital light professional services businesses that have high recurring revenue streams and strong cash flow generation. Aon drives its capital allocation decision making process around return on invested capital ("ROIC").

In 2015, 64% of our consolidated total revenues were in Risk Solutions and 37% of our consolidated total revenues were in HR Solutions, before intersegment eliminations.

BUSINESS SEGMENTS

Risk Solutions

The Risk Solutions segment generated approximately 64% of our consolidated total revenues in 2015, and has approximately 32,000 employees worldwide. We provide risk and insurance, as well as reinsurance, brokerage and related services in this segment.

Principal Products and Services

We operate in this segment through two similar transactional product lines: retail brokerage and reinsurance brokerage. In addition, a key component of this business is our risk consulting services.

Retail brokerage encompasses our retail brokerage services, affinity products, managing general underwriting, placement, captive management services and our Inpoint data and analytics solutions, including the Global Risk Insight Platform ("GRIP"). Our Americas operations provide products and services to clients in North, Central and South America, the Caribbean, and Bermuda. Our International operations in the U.K.; Europe, Middle East and Africa; and Asia Pacific offer these products and services to clients throughout the rest of the world.

Our employees draw upon our global network of resources, sophisticated data and analytics, and specialized expertise to deliver value to clients ranging from small and mid-sized businesses to multi-national corporations. We work with clients to identify their business needs and help them assess and understand their total cost of risk. Once we have gained an understanding of our clients' risk management needs, we seek to leverage our global network and implement a customized risk approach with local Aon resources. The outcome is intended to be a comprehensive risk solution provided locally and

personally. The Aon Client Promise® enables our colleagues around the globe to describe, benchmark and price the value we deliver to clients in a unified approach, based on the most important criteria that are critical to our clients' ability manage their total cost of risk.

Our knowledge and foresight, benchmarking and carrier knowledge are keys to providing professional services excellence. We intend to deliver superior value to clients and differentiation from competitors through our key Aon Broking initiatives, which positions us to provide our clients and insurers with additional market insight as well as new product offerings and facilities.

As a retail broker, we serve as an advisor to clients and facilitate a wide spectrum of risk management solutions for property liability, general liability, professional and directors' and officers' liability, workers' compensation, and various healthcare products, as well as other exposures. Our business is comprised of several specialty areas structured around specific product and industry needs.

We offer specialized advice and services in such industries as technology, financial services, agribusiness, aviation, construction, health care and energy, among others. Through our global affinity business, we provide products for professional liability, life, disability income and personal lines for individuals, associations and businesses around the world.

In addition, we are a major provider of risk consulting services, including captive management, that provide our clients with alternative vehicles for managing risks that would be cost-prohibitive or unavailable in traditional insurance markets.

Our health and benefits consulting practice advises clients about structuring, funding, and administering employee benefit programs, which attract, retain, and motivate employees. Benefits consulting and brokerage includes health and welfare, executive benefits, workforce strategies and productivity, absence management, data-driven health, compliance, employee commitment, and elective benefits services.

Reinsurance brokerage offers sophisticated advisory services in program design and claim recoveries intended to enhance the risk/return characteristics of insurance policy portfolios, improve capital utilization, and evaluate and mitigate catastrophic loss exposures worldwide. An insurance or reinsurance company may seek reinsurance or other risk-transfer solutions on all or a portion of the risks it insures. To accomplish this, our reinsurance brokerage services use dynamic financial analysis and capital market alternatives, such as transferring catastrophe risk through securitization. Reinsurance brokerage also offers capital management transaction and advisory services.

We act as a broker or intermediary for all classes of reinsurance. We place two main types of property and casualty reinsurance: treaty reinsurance, which involves the transfer of a portfolio of risks, and facultative reinsurance, which entails the transfer of part or all of the coverage provided by a single insurance policy. We also place specialty lines such as professional liability, workers' compensation, accident, life and health.

We also provide actuarial, enterprise risk management, catastrophe management and rating agency advisory services. We have developed tools and models that help our clients understand the financial implications of natural and man-made catastrophes around the world. Aon Securities Inc. provides global capital management transaction and advisory services for insurance and reinsurance clients. In this capacity, Aon Securities Inc. is recognized as a leader in:

In addition, our Inpoint business is a leading provider of consulting services to the insurance and reinsurance industry, helping carriers improve their performance to achieve growth and profitability.

Revenue and Compensation

Our Risk Solutions segment generates revenues primarily through commissions, fees from clients, and compensation from insurance and reinsurance companies for services we provide to them. Commission rates and fees vary depending upon several factors, which may include the amount of premium, the type of insurance or reinsurance coverage provided, the particular services provided to a client, insurer or reinsurer, and the capacity in which we act. Payment terms are consistent with current industry practice.

Fiduciary Funds

We typically hold funds on behalf of clients such as premiums received from clients and claims due to clients that are in transit to and from insurers. These funds held on behalf of clients are generally invested in interest-bearing premium trust accounts and can fluctuate significantly depending on when we collect cash from our clients and when premiums are remitted to the insurance carriers. We earn interest on these accounts; however, the principal is segregated and not available for general operating purposes.

Competition

Our Risk Solutions business operates in an environment that is highly competitive and very fragmented. We compete with other global insurance brokers, including Marsh & McLennan Companies, Inc., Willis Towers Watson Public Limited Company, Arthur J Gallagher & Company, and Jardine Lloyd Thompson Group plc, as well as numerous specialist, regional and local firms in almost every area of our business. We also compete with insurance and reinsurance companies that market and service their insurance products without the assistance of brokers or agents; and with other businesses that do not fall into the categories above, including commercial and investment banks, accounting firms, and consultants that provide risk-related services and products.

Seasonality

Our Risk Solutions segment typically experiences higher revenues in the first and fourth quarters of each year, primarily due to the timing of policy renewals.

HR Solutions

Our HR Solutions segment generated approximately 37% of our consolidated total revenues in 2015, and has approximately 31,000 employees worldwide with operations in the U.S., Canada, the U.K., Europe, and the Asia Pacific regions.

Principal Products and Services

We provide products and services in this segment primarily under the Aon Hewitt brand.

Our HR Solutions segment works to maximize the value of clients' human resources spending, increase employee productivity, and improve employee performance. Our approach addresses a trend towards more diverse workforces (demographics, nationalities, cultures and work/lifestyle preferences) that require more choices and flexibility among employers so that they can provide benefit options suited to individual needs.

We work with our clients to identify options in human resource outsourcing and process improvements. The primary areas where companies choose to use outsourcing services include benefits administration, core human resource processes, and workforce and talent management.

HR Solutions offers a broad range of human capital services in the following practice areas:

Retirement specializes in providing global actuarial services, defined contribution consulting, pension de-risking, tax and ERISA consulting, and pension administration.

Compensation focuses on compensation advisory/counsel including: compensation planning design, executive reward strategies, salary survey and benchmarking, market share studies and sales force effectiveness assessments, with special expertise in the financial services, technology, and life science industries.

Strategic Human Capital delivers advice to complex global organizations on talent, change and organizational effectiveness issues, including talent strategy and acquisition, executive on-boarding, performance management, leadership assessment and development, communication strategy, workforce training and change management.

Investment consulting provides public and private companies, other institutions and trustees with advice on developing and maintaining investment programs across a broad range of plan types, including defined benefit plans, defined contribution plans, endowments and foundations. In certain instances, we also perform delegated management services in relation to these plans.

Benefits Administration applies our HR expertise primarily through defined benefit, defined contribution, and health and welfare administrative services. We also provide other complementary services such as flexible spending, dependent audit and participant advocacy. Our model replaces the resource-intensive processes once required to administer benefit plans with more efficient, effective and less costly solutions.

Exchanges is building and operating health care exchanges that provide employers with a cost effective alternative to traditional employee and retiree healthcare, while helping individuals select the insurance that best meets their needs.

Human Resource Business Process Outsourcing ("HR BPO") provides market-leading traditional and cloud based solutions to deploy systems, manage employee data; administer benefits, payroll and other human resources processes; and record and manage talent, workforce and other core HR process transactions.

Revenue and Compensation

HR Solutions revenues are principally derived from fees paid by clients for advice and services. In addition, insurance companies pay us commissions for placing individual and group insurance contracts, primarily life, health and accident coverage, and pay us fees for consulting and other services that we provide to them. Payment terms are consistent with current industry practice.

Competition

Our HR Solutions business faces strong competition from other worldwide and national consulting companies, including Marsh & McLennan Companies, Inc. and Willis Towers Watson Public Limited Company. as well as regional and local firms. Competitors include independent consulting firms and consulting organizations affiliated with accounting, information systems, technology and financial services firms, large financial institutions and pure play outsourcers. Some of our competitors provide administrative or consulting services as an adjunct to other primary services. We believe that we are one of the leading providers of human capital services in the world.

Seasonality

Due to buying patterns and delivery of certain products in the markets we serve, revenues tend to be highest in the fourth quarter of each fiscal year.

Licensing and Regulation

Our business activities are subject to licensing requirements and extensive regulation under the laws of countries in which we operate, as well as U.S. federal and state laws. See the discussion contained in the "Risk Factors" section in Part I, Item 1A of this report for information regarding how actions by regulatory authorities or changes in legislation and regulation in the jurisdictions in which we operate may have an adverse effect on our business.

Risk Solutions

Regulatory authorities in the countries or states in the U.S. in which the operating subsidiaries of our Risk Solutions segment conduct business may require individual or company licensing to act as producers, brokers, agents, third party administrators, managing general agents, reinsurance intermediaries, or adjusters.

Under the laws of most countries and states, regulatory authorities have relatively broad discretion with respect to granting, renewing and revoking producers', brokers' and agents' licenses to transact business in the country or state. The operating terms may vary according to the licensing requirements of the particular country or state, which may require, among other things that a firm operates in the country or state through a local corporation. In a few countries and states, licenses may be issued only to individual residents or locally owned business entities. In such cases, our subsidiaries either have such licenses or have arrangements with residents or business entities licensed to act in the country or state.

Our subsidiaries must comply with laws and regulations of the jurisdictions in which they do business. These laws and regulations are enforced by the Financial Conduct Authority ("FCA") in the U.K., by federal and state agencies in the U.S., and by various regulatory agencies and other supervisory authorities in other countries through the granting and revoking of licenses to do business, licensing of agents, monitoring of trade practices, policy form approval, limits on commission rates and mandatory remuneration disclosure requirements.

Insurance authorities in the U.K., U.S. and certain other jurisdictions in which our subsidiaries operate also have enacted laws and regulations governing the investment of funds, such as premiums and claims proceeds, held in a fiduciary capacity for others. These laws and regulations generally require the segregation of these fiduciary funds and limit the types of investments that may be made with them.

Further, certain of our business activities within the Risk Solutions segment are governed by other regulatory bodies, including investment, securities and futures licensing authorities. For example, in the U.S., we use Aon Securities, Inc., a U.S.-registered broker-dealer and investment advisor, member of the Financial Industry Regulatory Authority ("FINRA") and Securities Investor Protection Corporation, and an indirect, wholly owned subsidiary of Aon, for capital management

transaction and advisory services and other broker-dealer activities. Similar operations exist in other jurisdictions outside of the U.S.

HR Solutions

Certain of the retirement-related consulting services provided by Aon Hewitt and its subsidiaries and affiliates are subject to the pension and financial laws and regulations of applicable jurisdictions, including oversight and/or supervision by the FCA in the U.K., the Securities and Exchange Commission ("SEC") in the U.S., and regulators in other countries. Aon Hewitt subsidiaries that provide investment advisory services are regulated by various U.S. federal authorities including the SEC and FINRA, as well as authorities on the state level. In addition, other services provided by Aon Hewitt and its subsidiaries and affiliates, such as trustee services and retirement and employee benefit program administrative services, are subject in various jurisdictions to pension, investment and securities and/or insurance laws and regulations and/or supervision by national regulators.

Clientele

Our clients operate in many businesses and industries throughout the world. No one client accounted for more than 1% of our consolidated total revenues in 2015. Additionally, we place insurance with many insurance carriers, none of which individually accounted for more than 10% of the total premiums we placed on behalf of our clients in 2015.

Segmentation of Activity by Type of Service and Geographic Area of Operation

Financial information relating to the types of services provided by us and the geographic areas of our operations is incorporated herein by reference to Note 15 "Segment Information" of the Notes to Consolidated Financial Statements in Part II, Item 8 of this report.

Employees

At December 31, 2015, we employed approximately 69,000 employees.

Information Concerning Forward-Looking Statements

This report and in reports we subsequently file or furnish and have previously filed or furnished with the SEC contains certain statements related to future results, or states our intentions, beliefs and expectations or predictions for the future which are forward-looking statements as that term is defined in the Private Securities Litigation Reform Act of 1995. Forward-looking statements relate to expectations or forecasts of future events. They use words such as "anticipate," "believe," "estimate," "expect," "forecast," "project," "intend," "plan," "probably," "potential," "looking forward," and other similar terms, and future or conditional tense verbs like "could," "may," "might," "should," "will" and "would." You can also identify forward-looking statements by the fact that they do not relate strictly to historical or current facts. For example, we may use forward-looking statements when addressing topics such as: market and industry conditions, including competitive and pricing trends; changes in our business strategies and methods of generating revenue; the development and performance of our services and products; changes in the composition or level of our revenues; our cost structure and the outcome of cost-saving or restructuring initiatives; the outcome of contingencies; dividend policy; the expected impact of acquisitions and dispositions; pension obligations; cash flow and liquidity; expected effective tax rate; future actions by regulators; and the impact of changes in accounting rules. These forward-looking statements are subject to certain risks and uncertainties that could cause actual results to differ materially from either historical or anticipated results depending on a variety of factors. Potential factors, which may be revised or supplemented in subsequent reports filed or furnished with the SEC, that could impact results include:

• changes in estimates or assumptions on our financial statements;

Any or all of our forward-looking statements may turn out to be inaccurate, and there are no guarantees about our performance. The factors identified above are not exhaustive. Aon and its subsidiaries operate in a dynamic business environment in which new risks may emerge frequently. Accordingly, readers should not place undue reliance on forward-looking statements, which speak only as of the dates on which they are made. We are under no obligation (and expressly disclaim any obligation) to update or alter any forward-looking statement that we may make from time to time, whether as a result of new information, future events or otherwise. Further information about factors that could materially affect Aon, including our results of operations and financial condition, is contained in the "Risk Factors" section in Part I, Item 1A of this report.

Website Access to Reports and Other Information

Our Annual Report on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K and all amendments to those reports are made available free of charge through our website (http://www.aon.com) as soon as practicable after such material is electronically filed with or furnished to the SEC. Additionally, the SEC maintains an internet site that contains reports, proxy and information statements, and other information. The address of the SEC's website is www.sec.gov. Also posted on our website are the charters for our Audit, Compliance, Organization and Compensation, Governance/Nominating and Finance Committees, our Governance Guidelines and our Code of Business Conduct. Within the time period required by the SEC and the New York Stock Exchange ("NYSE"), we will post on our website any amendment to or waiver of the Code of Business Conduct applicable to any executive officer or director. The information provided on our website is not part of this report and is therefore not incorporated herein by reference.

The risk factors set forth below reflect material risks associated with existing and potential lines of business and contain "forward-looking statements" as discussed in the "Business" Section of Part I, Item 1 of this report. Readers should consider them in addition to the other information contained in this report as our business, financial condition or results of operations could be adversely affected if any of these risks were to actually occur.

The following are material risks related to our businesses specifically and the industries in which we operate generally that could adversely affect our business, financial condition and results of operations and cause our actual results to differ materially from those stated in the forward-looking statements in this document and elsewhere. These risks are not presented in order of importance or probability of occurrence.

Risks Relating to the Company Generally

Competitive Risks

An overall decline in economic activity could have a material adverse effect on the financial condition and results of operations of our businesses.

The demand for property and casualty insurance generally rises as the overall level of economic activity increases and generally falls as such activity decreases, affecting both the commissions and fees generated by our Risk Solutions business. The economic activity that impacts property and casualty insurance is most closely correlated with employment levels, corporate revenue and asset values. Downward fluctuations in the year-over-year insurance premium charged by insurers to protect against the same risk, referred to in the industry as softening of the insurance market, could adversely affect our Risk Solutions business as a significant portion of the earnings are determined as a percentage of premium charged to our clients. A growing number of insolvencies and consolidation associated with an economic downturn, especially insolvencies in the insurance industry, could adversely affect our brokerage business through the loss of clients, by hampering our ability to place insurance and reinsurance business. Also, error and omission claims against us, which we refer to as E&O claims, generally increase in economic downturns, also adversely affecting our brokerage business.

The results of our HR Solutions business are generally affected by the level of business activity of our clients, which in turn is affected by the level of economic activity in the industries and markets these clients serve. Economic downturns in some markets may cause reductions in technology and discretionary spending by our clients, which may result in reductions in the growth of new business as well as reductions in existing business. If our clients become financially less stable, enter bankruptcy, liquidate their operations or consolidate, our revenues and/or collectability of receivables could be adversely affected. In addition, our revenues from many of our outsourcing contracts depend upon the number of our clients' employees or the number of participants in our clients' employee benefit plans and could be adversely affected by layoffs. We may also experience decreased demand for our services as a result of postponed or terminated outsourcing of human resources functions. Reduced demand for our services could increase price competition.

We face significant competitive pressures in each of our businesses.

We believe that competition in our Risk Solutions segment is based on service, product features, price, commission structure, financial strength, ability to access certain insurance markets and name recognition. In this regard, we compete with a large number of global, national, regional and local insurance companies and other financial services providers and brokers.

Our HR Solutions segment competes with a large number of independent firms and consulting organizations affiliated with accounting, information systems, technology and financial services firms around the world. Many of our competitors in this area are expanding the services they offer or reducing prices in an attempt to gain additional business. Additionally, some competitors have established, and are likely to continue to establish, cooperative relationships among themselves or with third parties to increase their ability to address client needs.

Our competitors may have greater financial, technical and marketing resources, larger customer bases, greater name recognition, stronger presence in certain geographies and more established relationships with their customers and suppliers than we have. In addition, new competitors, alliances among competitors or mergers of competitors could emerge and gain significant market share, and some of our competitors may have or may develop a lower cost structure, adopt more aggressive pricing policies or provide services that gain greater market acceptance than the services that we offer or develop. Large and well-capitalized competitors may be able to respond to the need for technological changes and innovate faster, or price their services more aggressively. They may also compete for skilled professionals, finance acquisitions, fund internal growth and compete for market share more effectively than we do. To respond to increased competition and pricing pressure, we may have to lower the cost of our services or decrease the level of service provided to clients, which could have an adverse effect on our financial condition or results of operations.

Financial Risks

We are exposed to fluctuations in currency exchange rates that could negatively impact our financial results and cash flows.

We face exposure to adverse movements in exchange rates of currencies other than our reporting currency, the U.S. Dollar, as a significant portion of our business is located outside of the United States. These exposures may change over time, and they could have a material adverse impact on our financial results and cash flows. Our five largest non-U.S. Dollar exposures are the British Pound, Euro, Australian Dollar, Canadian Dollar and Indian Rupee; however, we also have exposures to other currencies which can have significant currency volatility. These currency exchange risks are present in both the translation of the financial results of our global subsidiaries into U.S. Dollars for our consolidated financial statements, as well as those of our operations that receive revenue and incur expenses other than in their respective local currencies which can reduce the profitability of our operations based on the direction the respective currencies' exchange rates move. A decrease in the value of certain currencies relative to other currencies could place us at a competitive disadvantage compared to our competitors that benefit to a greater degree from a specific exchange rate move and can, as a result, deliver services at a lower cost or receive greater revenues from such a transaction. Although we use various derivative financial instruments to help protect against adverse foreign exchange rate fluctuations, we cannot eliminate such risks, and, as a result, changes in exchange rates may adversely affect our results. For example, the strengthening of the value of the U.S. dollar versus other currencies might adversely affect the value of our products and services when translated to U.S. dollar, even if the value of such products and services has not changed in their original currency.

Changes in interest rates and deterioration of credit quality could reduce the value of our cash balances and investment portfolios and adversely affect our financial condition or results.

Operating funds available for corporate use were $740 million at December 31, 2015 and are reported in Cash and cash equivalents and Short-term investments. Funds held on behalf of clients and insurers were $3.4 billion at December 31, 2015 and are reported in Fiduciary assets. We also carry an investment portfolio of other long-term investments.

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None.

We have offices in various locations throughout the world. Substantially all of our offices are located in leased premises. We maintain our corporate headquarters at 122 Leadenhall Street, London, England, where we occupy approximately 190,000 square feet of space under an operating lease agreement that expires in 2034. We own one significant building at Pallbergweg 2-4, Amsterdam, the Netherlands (150,000 square feet). The following are additional significant leased properties, along with the occupied square footage and expiration.

The locations in Lincolnshire, Illinois, Gurgaon, India, The Woodlands, Texas, Orlando, Florida, and Charlotte, North Carolina, are primarily dedicated to our HR Solutions segment. The other locations listed above house personnel from both of our reportable segments.

In general, no difficulty is anticipated in negotiating renewals as leases expire or in finding other satisfactory space if the premises become unavailable. We believe that the facilities we currently occupy are adequate for the purposes for which they are being used and are well maintained. In certain circumstances, we may have unused space and may seek to sublet such space to third parties, depending upon the demands for office space in the locations involved. See Note 7 "Lease Commitments" of the Notes to Consolidated Financial Statements in Part II, Item 8 of this report for information with respect to our lease commitments as of December 31, 2015.

We hereby incorporate by reference Note 14 "Commitments and Contingencies" of the Notes to Consolidated Financial Statements in Part II, Item 8 of this report.

Not applicable.

Executive Officers of the Registrant

The executive officers of Aon, their business experience during the last five years, and their ages and positions held are set forth below.

PART II

Our Class A Ordinary Shares, $0.01 nominal value per share, are traded on the New York Stock Exchange. We hereby incorporate by reference the "Dividends paid per share" and "Price range" data in Note 17 "Quarterly Financial Data" of the Notes to Consolidated Financial Statements in Part II, Item 8 of this report.

We have approximately 241 holders of record of our Class A Ordinary Shares as of February 5, 2016.

We hereby incorporate by reference Note 9, "Shareholders' Equity" of the Notes to Consolidated Financial Statements in Part II, Item 8 of this report.

The following information relates to the repurchases of equity securities by Aon or any affiliated purchaser during any month within the fourth quarter of the fiscal year covered by this report:

(1)In April 2012, our Board of Directors authorized a share repurchase program under which up to $5 billion of Class A Ordinary Shares may be repurchased. In November 2014, our Board of Directors authorized an additional $5 billion of Class A Ordinary Shares for repurchase. Under each program, shares may be repurchased through open market or privately negotiated transactions, based on prevailing market conditions, funded from available capital. During 2015, we repurchased 16.0 million shares at an average price per share of $97.04 for a total cost of $1.6 billion. The remaining authorized amount for share repurchase under our Share Repurchase Programs is $4.1 billion.

Information relating to the compensation plans under which equity securities of Aon are authorized for issuance is set forth under Part III, Item 12 "Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters" of this report and is incorporated herein by reference.

We did not make any sales of unregistered equity in 2015.

Selected Financial Data

EXECUTIVE SUMMARY OF 2015 FINANCIAL RESULTS

During 2015, we continued to face headwinds that had adversely impacted our business in prior periods. In our Risk Solutions segment, these headwinds included adverse changes in foreign currency exchange rates, economic weakness in continental Europe and a negative market impact in our Reinsurance business. In our HR Solutions segment, these headwinds included price compression in our benefits administration business and economic weakness in continental Europe.

The following is a summary of our 2015 financial results:

We focus on four key non-GAAP metrics that we communicate to shareholders: organic revenue, adjusted operating margins, adjusted diluted earnings per share, and free cash flow. The following is our measure of performance against these four metrics for 2015:

per share in 2015, an increase of $0.47 per share, or 8%, from $5.71 per share in 2014. The increase demonstrates solid operational performance and effective capital management, highlighted by $1.6 billion of share repurchase during 2015.

REVIEW OF CONSOLIDATED RESULTS

General

In our discussion of operating results, we sometimes refer to certain non-GAAP supplemental information derived from consolidated financial information specifically related to organic revenue growth, adjusted operating margin, adjusted diluted earnings per share, free cash flow, and the impact of foreign exchange rate fluctuations on operating results.

Organic Revenue

We use supplemental information related to organic revenue to help us and our investors evaluate business growth from existing operations. Organic revenue is a non-GAAP measure and excludes the impact of foreign exchange rate changes, acquisitions, divestitures, transfers between business units, fiduciary investment income, reimbursable expenses, and certain unusual items. Supplemental information related to organic revenue growth represents a measure not in accordance with U.S. GAAP, and should be viewed in addition to, not instead of, our Consolidated Financial Statements and Notes thereto. Industry peers provide similar supplemental information about their revenue performance, although they may not make identical adjustments. Reconciliations of this non-GAAP measure, organic revenue growth percentages, to the reported Commissions, fees and other revenue growth percentages, have been provided under the "Review by Segment" caption below.

Adjusted Operating Margins

We use adjusted operating margins as a non-GAAP measure of core operating performance of our Risk Solutions and HR Solutions segments. Adjusted operating margins exclude the impact of certain items, including intangible asset amortization, litigation settlements, and restructuring charges because management does not believe these expenses reflect our core operating performance. This supplemental information related to adjusted operating margin represents a measure not in accordance with U.S. GAAP, and should be viewed in addition to, not instead of, our Consolidated Financial Statements and Notes thereto.

A reconciliation of this non-GAAP measure to reported operating margins is as follows (in millions):

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We are exposed to potential fluctuations in earnings, cash flows, and the fair value of certain of our assets and liabilities due to changes in interest rates and foreign exchange rates. To manage the risk from these exposures, we enter into a variety of derivative instruments. We do not enter into derivatives or financial instruments for trading or speculative purposes.

The following discussion describes our specific exposures and the strategies we use to manage these risks. See Note 2 "Summary of Significant Accounting Principles and Practices" of the Notes to Consolidated Financial Statements for a discussion of our accounting policies for financial instruments and derivatives.

Foreign Exchange Risk

We are subject to foreign exchange rate risk. Our primary exposures include exchange rates between the U.S. dollar and the euro, the British pound, the Canadian dollar, the Australian dollar, and the Indian rupee. We use over-the-counter options and forward contracts to reduce the impact of foreign currency risk to our financial statements.

Additionally, some of our non-U.S. brokerage subsidiaries receive revenues in currencies that differ from their functional currencies. Our U.K. subsidiaries earn a portion of their revenue in U.S. dollars and euros, but most of their expenses are incurred in British pounds. At December 31, 2015, we have hedged approximately 45% of our U.K. subsidiaries' expected exposures to both U.S. dollar and euro transactions for the years ending December 31, 2016 and 2017, respectively. We generally do not hedge exposures beyond three years.

We also use forward contracts to economically hedge foreign exchange risk associated with monetary balance sheet exposures, such as inter-company notes and short-term assets and liabilities that are denominated in a non-functional currency and are subject to remeasurement.

The potential loss in future earnings from foreign exchange derivative instruments resulting from a hypothetical 10% adverse change in year-end exchange rates would be $32 million and $14 million at December 31, 2016 and 2017 respectively.

Interest Rate Risk

Our fiduciary investment income is affected by changes in international and domestic short-term interest rates. We monitor our net exposure to short-term interest rates, and as appropriate, hedge our exposure with various derivative financial instruments. This activity primarily relates to brokerage funds held on behalf of clients in the North America, continental Europe, and the Asia Pacific region. A hypothetical, instantaneous parallel decrease in the year-end yield curve of 100 basis points would cause a decrease, net of derivative positions, of $39 million and $41 million to 2016 and 2017 pretax income, respectively. A corresponding increase in the year-end yield curve of 100 basis points would cause an increase, net of derivative positions, of $39 million and $41 million to 2016 and 2017 pretax income, respectively.

We have long-term debt outstanding with a fair market value of $5.4 billion and $5.3 billion at December 31, 2015 and 2014, respectively. This fair value was greater than the carrying value by $0.2 billion at December 31, 2015, and $0.5 billion greater than the carrying value at December 31, 2014. A hypothetical 1% increase or decrease in interest rates would change the fair value by a decrease of 10% or an increase of 11%, respectively, at December 31, 2015.

We have selected hypothetical changes in foreign currency exchange rates, interest rates, and equity market prices to illustrate the possible impact of these changes; we are not predicting market events.

Report of Independent Registered Public Accounting Firm

Board of Directors and Shareholders

Aon plc

We have audited the accompanying consolidated statements of financial position of Aon plc as of December 31, 2015 and 2014, and the related consolidated statements of income, comprehensive income, shareholders' equity, and cash flows for each of the three years in the period ended December 31, 2015. These financial statements are the responsibility of the Company's management. Our responsibility is to express an opinion on these financial statements based on our audits.

We conducted our audits in accordance with the standards of the Public Company Accounting Oversight Board (United States). Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement. An audit includes examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements. An audit also includes assessing the accounting principles used and significant estimates made by management, as well as evaluating the overall financial statement presentation. We believe that our audits provide a reasonable basis for our opinion.

In our opinion, the financial statements referred to above present fairly, in all material respects, the consolidated financial position of Aon plc at December 31, 2015 and 2014, and the consolidated results of its operations and its cash flows for each of the three years in the period ended December 31, 2015, in conformity with U.S. generally accepted accounting principles.

We also have audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States), Aon plc's internal control over financial reporting as of December 31, 2015, based on criteria established in Internal Control-Integrated Framework issued by the Committee of Sponsoring Organizations of the Treadway Commission (2013 Framework) and our report dated February 22, 2016 expressed an unqualified opinion thereon.

Chicago, Illinois

February 22, 2016

Aon plc

Consolidated Statements of Income

See accompanying Notes to Consolidated Financial Statements.

Aon plc

Consolidated Statements of Comprehensive Income

See accompanying Notes to Consolidated Financial Statements.

Aon plc

Consolidated Statements of Financial Position

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None.

Evaluation of Disclosure Controls and Procedures

We have conducted an evaluation of the effectiveness of the design and operation of our disclosure controls and procedures, as defined in Rules 13a-15(e) and 15d-15(e) under the Securities Exchange Act of 1934, as amended (the "Exchange Act") as of the end of the period covered by this annual report of December 31, 2015. Based on this evaluation, our chief executive officer and chief financial officer concluded as of December 31, 2015 that our disclosure controls and procedures were effective such that the information relating to Aon, including our consolidated subsidiaries, required to be disclosed in our SEC reports is recorded, processed, summarized and reported within the time periods specified in SEC rules and forms, and is accumulated and communicated to Aon's management, including our chief executive officer and chief financial officer, as appropriate to allow timely decisions regarding required disclosure.

Management's Report on Internal Control Over Financial Reporting

Management of Aon plc is responsible for establishing and maintaining adequate internal control over financial reporting as defined in Rules 13a-15(f) and 15d-15(f) under the Exchange Act. The Company's internal control over financial reporting is designed to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with U.S. generally accepted accounting principles. Because of its inherent limitations, internal control over financial reporting may not prevent or detect misstatements. Also, projections of any evaluation of effectiveness to future periods are subject to the risk that controls may become inadequate because of changes in conditions, or that the degree of compliance with the policies or procedures may deteriorate.

Under the supervision and with the participation of our senior management, including our chief executive officer and chief financial officer, we assessed the effectiveness of our internal control over financial reporting as of December 31, 2015. In making this assessment, we used the criteria set forth by the Committee of Sponsoring Organizations of the Treadway Commission (COSO) in the Internal Control — Integrated Framework (2013 Framework). Based on this assessment, management has concluded our internal control over financial reporting is effective as of December 31, 2015.

The effectiveness of our internal control over financial reporting as of December 31, 2015 has been audited by Ernst & Young, LLP, the Company's independent registered public accounting firm, as stated in their report titled "Report of Independent Registered Public Accounting Firm on Internal Control Over Financial Reporting."

Changes in Internal Control Over Financial Reporting

No changes in Aon's internal control over financial reporting (as defined in Rule 13a-15(f) under the Exchange Act) occurred during 2015 that have materially affected, or that are reasonably likely to materially affect, Aon's internal control over financial reporting.

Report of Independent Registered Public Accounting Firm on Internal Control Over Financial Reporting

Board of Directors and Shareholders

Aon plc

We have audited Aon plc's internal control over financial reporting as of December 31, 2015, based on criteria established in Internal Control — Integrated Framework issued by the Committee of Sponsoring Organizations of the Treadway Commission (2013 Framework) (the COSO criteria). Aon plc's management is responsible for maintaining effective internal control over financial reporting, and for its assessment of the effectiveness of internal control over financial reporting included in the accompanying Management's Report on Internal Control over Financial Reporting. Our responsibility is to express an opinion on the company's internal control over financial reporting based on our audit.

We conducted our audit in accordance with the standards of the Public Company Accounting Oversight Board (United States). Those standards require that we plan and perform the audit to obtain reasonable assurance about whether effective internal control over financial reporting was maintained in all material respects. Our audit included obtaining an understanding of internal control over financial reporting, assessing the risk that a material weakness exists, testing and evaluating the design and operating effectiveness of internal control based on the assessed risk, and performing such other procedures as we considered necessary in the circumstances. We believe that our audit provides a reasonable basis for our opinion.

A company's internal control over financial reporting is a process designed to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles. A company's internal control over financial reporting includes those policies and procedures that (1) pertain to the maintenance of records that, in reasonable detail, accurately and fairly reflect the transactions and dispositions of the assets of the company; (2) provide reasonable assurance that transactions are recorded as necessary to permit preparation of financial statements in accordance with generally accepted accounting principles, and that receipts and expenditures of the company are being made only in accordance with authorizations of management and directors of the company; and (3) provide reasonable assurance regarding prevention or timely detection of unauthorized acquisition, use or disposition of the company's assets that could have a material effect on the financial statements.

Because of its inherent limitations, internal control over financial reporting may not prevent or detect misstatements. Also, projections of any evaluation of effectiveness to future periods are subject to the risk that controls may become inadequate because of changes in conditions or that the degree of compliance with the policies or procedures may deteriorate.

In our opinion, Aon plc maintained, in all material respects, effective internal control over financial reporting as of December 31, 2015, based on the COSO criteria.

We also have audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States), the consolidated statements of financial position of Aon plc as of December 31, 2015 and 2014, and the related consolidated statements of income, comprehensive income, shareholders' equity and cash flows for each of the three years in the period ended December 31, 2015 and our report dated February 22, 2016 expressed an unqualified opinion thereon.

Chicago, Illinois

February 22, 2016

Not applicable.

PART III

Information relating to Aon's Directors is set forth under the heading "Proposal 1 — Resolutions Regarding the Election of Directors" in our Proxy Statement for the 2016 Annual General Meeting of Shareholders to be held on June 24, 2016 (the "Proxy Statement") and is incorporated herein by reference from the Proxy Statement. Information relating to the executive officers of Aon is set forth in Part I of this Form 10-K and is incorporated by reference. Information relating to compliance with Section 16(a) of the Exchange Act is incorporated by reference from the discussion under the heading "Section 16(a) Beneficial Ownership Reporting Compliance" in the Proxy Statement. The remaining information called for by this item is incorporated herein by reference to the information under the heading "Corporate Governance" and the information under the heading "Board of Directors and Committees" in the Proxy Statement.

We have adopted a code of ethics that applies to the Company’s directors, officers and employees, including the Chief Executive Officer, Chief Financial Officer, Controller and Chief Accounting Officer and other persons performing similar functions. The text of our code of ethics, which we call our Code of Business Conduct, is available on our website as disclosed in Item 1 of this report. We will provide a copy of the code of ethics without charge upon request to the Company Secretary, Aon plc, 122 Leadenhall Street, London EC3V 4AN, United Kingdom. We will disclose on our website any amendment to or waiver from our code of ethics on behalf of any of our executive officers or directors.

Information relating to director and executive officer compensation is set forth under the headings "Compensation Committee Report," "Compensation Discussion and Analysis," and "Executive Compensation" in the Proxy Statement, and all such information is incorporated herein by reference.

The material incorporated herein by reference to the information set forth under the heading "Compensation Committee Report" in the Proxy Statement shall be deemed furnished, and not filed, in this Form 10-K and shall not be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act as a result of this furnishing, except to the extent that it is specifically incorporated by reference by Aon.

Information relating to compensation committee interlocks and insider participation is incorporated by reference to the information under the heading "Compensation Discussion and Analysis - Compensation Committee Interlocks and Insider Participation" in the Proxy Statement.

Information relating to equity compensation plans and the security ownership of certain beneficial owners and management of Aon's ordinary shares is set forth under the headings "Equity Compensation Plan Information", "Principal Holders of Voting Securities" and "Security Ownership of Directors and Executive Officers" in the Proxy Statement and all such information is incorporated herein by reference.

Aon hereby incorporates by reference the information under the headings "Corporate Governance — Director Independence" and "Certain Relationships and Related Transactions" in the Proxy Statement.

Information required by this Item is included under the caption "Auditor Fees" in the Proxy Statement and is hereby incorporated by reference.

PART IV

The following document has been included in Part II, Item 9.

All schedules for the Registrant and consolidated subsidiaries have been omitted because the required information is not present in amounts sufficient to require submission of the schedules or because the information required is included in the respective financial statements or notes thereto.

• Document has been previously filed with the Securities and Exchange Commission and is incorporated herein by reference herein. Unless otherwise indicated, such document was filed under Commission File Number 001-07933.

Indicates a management contract or compensatory plan or arrangement.

The registrant agrees to furnish to the Securities and Exchange Commission upon request a copy of (1) any long-term debt instruments that have been omitted pursuant to Item 601(b)(4)(iii)(A) of Regulation S-K, and (2) any schedules omitted with respect to any material plan of acquisition, reorganization, arrangement, liquidation or succession set forth above.

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Pursuant to the requirements of the Securities Exchange Act of 1934, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

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