Item 6. Selected Financial Data

(a) The above results for 2020 include a $367.9 million pre-tax charge ($305.1 million, net of tax) related to a litigation settlement. The above results for 2019 include special charges of $64.6 million ($58.7 million, net of tax), primarily the impairment of certain assets and the acquisition of early-stage intellectual property. The above results for 2018 include special charges of $109.1 million ($103.0 million, net of tax), primarily the impairment of intangible assets and a $180.0 million ($137.5 million, net of tax) charge related to a litigation settlement. The above results for 2017 include a $112.5 million ($70.3 million, net of tax) gain for a litigation payment received in 2017 and a $262.0 million tax expense related to the implementation of U.S. tax law changes. See Part II, Item 7, "Management's Discussion and Analysis of Financial Condition and Results of Operations" and Note 3, Note 4, and Note 17 to the "Consolidated Financial Statements" for additional information.

(b) In October 2013, we issued $600.0 million of 2.875% fixed-rate unsecured senior notes due October 15, 2018 (the "2013 Notes"). At December 31, 2017, the 2013 Notes were classified as short-term obligations as these obligations were due within one year. These 2013 Notes were paid in October 2018. In June 2018, we issued $600.0 million of 4.3% fixed-rate unsecured senior notes due June 15, 2028, which were classified as long-term obligations as of December 31, 2020, 2019 and 2018. Amounts outstanding under our Five-Year Credit Agreement ("Credit Agreement") have been classified as long-term obligations in accordance with the terms of the Credit Agreement.

(c) The per share amounts for the prior periods presented have been retroactively adjusted to reflect the three-for-one stock split effected in the second quarter of 2020.