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	1,744				1,744
Foreign currency translation adjustments, net of tax	(28)					(28)
Net unrealized gains on available-for-sale securities, net of tax	114					114
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)		195
Exercise of stock options and vesting of restricted stock units and performance share units	$ 1	$ 0		1
Repurchase of common stock (in shares)	(3,061)		(3,061)
Repurchase of common stock	$ (5,462)		$ (5,462)
Stock-based compensation and other stock-based payments	153			153
Balance (in shares) at Jun. 30, 2019		63,144	(20,378)
Balance at Jun. 30, 2019	5,307	$ 0	$ (20,173)	5,599	20,111	(230)
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)
Increase (Decrease) in Stockholders' Equity
Net (loss) income	979				979
Foreign currency translation adjustments, net of tax	(16)					(16)
Net unrealized gains on available-for-sale securities, net of tax	(45)					(45)
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)		22
Exercise of stock options and vesting of restricted stock units and performance share units	$ 1	$ 0		1
Repurchase of common stock (in shares)	(1,442)		(1,442)
Repurchase of common stock	$ (2,606)		$ (2,606)
Stock-based compensation and other stock-based payments	79			79
Balance (in shares) at Jun. 30, 2019		63,144	(20,378)
Balance at Jun. 30, 2019	5,307	$ 0	$ (20,173)	5,599	20,111	(230)
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	(577)				(577)
Foreign currency translation adjustments, net of tax	(45)					(45)
Net unrealized gains on available-for-sale securities, net of tax	3					3
Issuance of convertible senior notes	96			96
Conversion of debt	(245)			(245)
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)		212
Exercise of stock options and vesting of restricted stock units and performance share units	$ 6	$ 0		6
Repurchase of common stock (in shares)	(680)		(680)
Repurchase of common stock	$ (1,255)		$ (1,255)
Stock-based compensation and other stock-based payments	86			86
Balance (in shares) at Jun. 30, 2020		63,391	(22,442)
Balance at Jun. 30, 2020	3,999	$ 0	$ (24,119)	5,699	22,652	(233)
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)
Increase (Decrease) in Stockholders' Equity
Net (loss) income	122				122
Foreign currency translation adjustments, net of tax	32					32
Net unrealized gains on available-for-sale securities, net of tax	77					77
Issuance of convertible senior notes	96			96
Conversion of debt	(241)			(241)
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)		21
Exercise of stock options and vesting of restricted stock units and performance share units	$ 6	$ 0		6
Repurchase of common stock (in shares)	(2)		(2)
Repurchase of common stock	$ (4)		$ (4)
Stock-based compensation and other stock-based payments	80			80
Balance (in shares) at Jun. 30, 2020		63,391	(22,442)
Balance at Jun. 30, 2020	$ 3,999	$ 0	$ (24,119)	$ 5,699	$ 22,652	$ (233)