UNAUDITED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Millions	Total	Cumulative Effect of Adoption of Accounting Standards Update	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Retained Earnings Cumulative Effect of Adoption of Accounting Standards Update	Accumulated Other Comprehensive Loss
Balance (in shares) at Dec. 31, 2019			63,179	(21,762)
Balance at Dec. 31, 2019	$ 5,933	$ (3)	$ 0	$ (22,864)	$ 5,756	$ 23,232	$ (3)	$ (191)
Increase (Decrease) in Stockholders' Equity
Net loss	(699)					(699)
Foreign currency translation adjustments	(77)							(77)
Unrealized losses on cash flow hedges	0
Net unrealized losses on available-for-sale securities	(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)
Balance (in shares) at Dec. 31, 2020			63,406	(22,447)
Balance at Dec. 31, 2020	4,893		$ 0	$ (24,128)	5,851	23,288		(118)
Increase (Decrease) in Stockholders' Equity
Net loss	(55)					(55)
Foreign currency translation adjustments	(30)							(30)
Unrealized losses on cash flow hedges	(11)							(11)
Net unrealized losses on available-for-sale securities	(1)							(1)
Exercise of stock options and vesting of restricted stock units and performance share units (in shares)			156
Exercise of stock options and vesting of restricted stock units and performance share units	$ 1		$ 0		1
Repurchase of common stock (in shares)	(64)			(64)
Repurchase of common stock	$ (146)			$ (146)
Stock-based compensation and other stock-based payments	113				113
Balance (in shares) at Mar. 31, 2021			63,562	(22,511)
Balance at Mar. 31, 2021	$ 4,764		$ 0	$ (24,274)	$ 5,965	$ 23,233		$ (160)