Item 6. Selected Financial Data

The data presented in the following table is derived from the audited consolidated financial statements and other information.

SELECTED FINANCIAL DATA



	Year Ended December 31
$ in millions, except per share amounts	2019		2018(1)		2017		2016		2015(2)
Sales	$	33,841	$	30,095	$	26,004	$	24,706	$	23,526
Operating income	3,969		3,780		3,218		3,277		2,984
Net earnings	2,248		3,229		2,869		2,043		2,119
Basic earnings per share	$	13.28	$	18.59	$	16.45	$	11.42	$	11.19
Diluted earnings per share	13.22		18.49		16.34		11.32		11.06
Cash dividends declared per common share	5.16		4.70		3.90		3.50		3.10
Year-End Financial Position
Total assets(3)	$	41,089	$	37,653	$	35,128	$	25,815	$	24,424
Notes payable to banks and long-term debt	13,879		14,400		15,266		7,070		6,496
Other long-term obligations(3)(4)	10,066		7,309		6,505		7,667		7,059
Financial Metrics
Net cash provided by operating activities	$	4,297	$	3,827	$	2,613	$	2,813	$	2,162
Free cash flow(5)	3,033		2,578		1,685		1,893		1,691
Other Information
Company-sponsored research and development expenses	$	953	$	764	$	639	$	705	$	712
Total backlog(6)	64,840		53,500		42,629		45,339		35,923
Square footage at year-end (in thousands)	53,780		53,283		35,379		34,112		34,392
Number of employees at year-end	90,000		85,000		70,000		67,000		65,000


(1)	Selected financial data includes the operating results of Innovation Systems subsequent to the Merger date.


(2)	Years prior to 2016 do not reflect the effects from our January 1, 2018 adoption of ASC Topic 606, Revenue from Contracts with Customers.


(3)	We adopted ASC Topic 842, Leases, on January 1, 2019 using the optional transition method and, as a result, did not recast prior period consolidated comparative financial statements.


(4)	Other long-term obligations include pension and other postretirement benefit (OPB) plan liabilities, operating lease liabilities, deferred tax liabilities and other non-current liabilities, including unrecognized tax benefits, deferred compensation and environmental liabilities.


(5)	Free cash flow is a non-GAAP measure. See “Liquidity and Capital Resources” – “Free Cash Flow” in Management’s Discussion and Analysis of Financial Conditions and Results of Operations (MD&A) for our definition of this measure, including a reconciliation of free cash flow to net cash provided by operating activities.


(6)	We applied the ASC Topic 606 transition practical expedient related to remaining performance obligations for reporting periods presented before the date of initial application. As such, years prior to 2017 have not been restated for the adoption of ASC Topic 606. For comparative purposes, we have recast our backlog as of December 31, 2017 to reflect the impact of ASC Topic 606.

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NORTHROP GRUMMAN CORPORATION