UNAUDITED CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Balance (in shares) at Dec. 31, 2018		62,949	(17,317)
Balance at Dec. 31, 2018	$ 8,785	$ 0	$ (14,711)	$ 5,445	$ 18,367	$ (316)
Increase (Decrease) in Stockholders' Equity
Net (loss) income	765				765
Foreign currency translation adjustments, net of taxes	(12)					(12)
Net unrealized gains (losses) on debt securities, net of taxes	159					159
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)		173
Exercise of stock options and vesting of restricted stock units and performance share units	$ 0	$ 0		0
Repurchase of common stock (in shares)	(1,619)		(1,619)
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	(18,936)
Balance at Mar. 31, 2019	6,915	$ 0	$ (17,567)	5,519	19,132	(169)
Balance (in shares) at Dec. 31, 2019		63,179	(21,762)
Balance at Dec. 31, 2019	5,933	$ 0	$ (22,864)	5,756	23,232	(191)
Increase (Decrease) in Stockholders' Equity
Net (loss) income	(699)				(699)
Foreign currency translation adjustments, net of taxes	(77)					(77)
Net unrealized gains (losses) on debt securities, net of taxes	(74)					(74)
Reclassification adjustment for convertible debt in mezzanine	(4)			(4)
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)		191
Exercise of stock options and vesting of restricted stock units and performance share units	$ 0	$ 0		0
Repurchase of common stock (in shares)	(678)		(678)
Repurchase of common stock	$ (1,251)		$ (1,251)
Stock-based compensation and other stock-based payments	6			6
Balance (in shares) at Mar. 31, 2020		63,370	(22,440)
Balance at Mar. 31, 2020	$ 3,831	$ 0	$ (24,115)	$ 5,758	$ 22,530	$ (342)