UNAUDITED CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Millions		Total		Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity
Cumulative effect of adoption of accounting standards updates		$ 189					$ 430	$ (241)
Balance (in shares) at Dec. 31, 2017				62,689,000	(14,217,000)
Balance at Dec. 31, 2017		11,261		$ 0	$ (8,699)	$ 5,783	13,939	238
Increase (Decrease) in Stockholders' Equity
Net income		607	[1]				607
Foreign currency translation adjustments, net of taxes		61	[2]					61
Net unrealized gains (losses) on marketable securities, net of taxes	[1]	0
Reclassification adjustment for convertible debt in mezzanine		(48)				(48)
Exercise of stock options and vesting of restricted stock units and/or performance share units (in shares)				149,000
Exercise of stock options and vesting of restricted stock units and/or performance share units		$ 0		$ 0		0
Repurchase of common stock (in shares)		(373,119)			(373,000)
Repurchase of common stock		$ (732)			$ (732)
Stock-based compensation and other stock-based payments		71				71
Conversion of debt		(773)				(773)
Balance (in shares) at Mar. 31, 2018				62,838,000	(14,590,000)
Balance at Mar. 31, 2018		10,636		$ 0	$ (9,431)	5,033	14,976	58
Balance (in shares) at Dec. 31, 2018				62,949,000	(17,317,000)
Balance at Dec. 31, 2018		8,785		$ 0	$ (14,711)	5,445	18,367	(316)
Increase (Decrease) in Stockholders' Equity
Net income		765	[1]				765
Foreign currency translation adjustments, net of taxes		(12)	[2]					(12)
Net unrealized gains (losses) on marketable securities, net of taxes		159	[1]					159
Exercise of stock options and vesting of restricted stock units and/or performance share units (in shares)				173,000
Exercise of stock options and vesting of restricted stock units and/or performance share units		$ 0		$ 0		0
Repurchase of common stock (in shares)		(1,618,788)			(1,619,000)
Repurchase of common stock		$ (2,856)			$ (2,856)
Stock-based compensation and other stock-based payments		74				74
Balance (in shares) at Mar. 31, 2019				63,122,000	(18,936,000)
Balance at Mar. 31, 2019		$ 6,915		$ 0	$ (17,567)	$ 5,519	$ 19,132	$ (169)

[1] The Company realized net gains of $1 million for the three months ended March 31, 2019 from sales of investments in debt securities.

[2] Foreign currency translation adjustments result from currency fluctuations on the translation of the Company's non-U.S. Dollar denominated net assets, net of the impact of net investment hedges. During the three months ended March 31, 2019 and 2018, the Company recorded a tax benefit of $11 million and a tax charge of $10 million, respectively, related to foreign currency translation adjustments to its one-time deemed repatriation tax liability recorded at December 31, 2017 and foreign earnings for periods after December 31, 2017 that are subject to U.S. federal and state income tax, resulting from the introduction of the U.S. Tax Cuts and Jobs Act (the "Tax Act"). Foreign currency translation adjustments also include a tax charge of $19 million and a tax benefit of $26 million for the three months ended March 31, 2019 and 2018, respectively, associated with the Company's Euro-denominated debt, which was designated as a net investment hedge against the impact of currency fluctuations on the Company's Euro-denominated net assets (see Note 9).