Consolidated Statements of Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings
Beginning Balance (shares) at Dec. 31, 2018		169,499,000
Beginning Balance at Dec. 31, 2018	$ 12,111	$ 2	$ 9,062	$ (423)	$ 3,470
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared	(54)				(54)
Exercise of long-term incentive stock options		10,000
Exercise of employee stock purchases	0		(1)	1
Purchases of treasury stock (shares)		(1,594,000)
Purchases of treasury stock	(222)			(222)
Stock-based compensation costs:
Issued awards (shares)		507,000
Issued awards	0
Compensation costs included in net loss	24		24
Net income	350				350
Issued awards (shares)		507,000
Issued awards	0
Ending Balance (shares) at Mar. 31, 2019		168,422,000
Ending Balance at Mar. 31, 2019	12,209	$ 2	9,085	(644)	3,766
Beginning Balance (shares) at Dec. 31, 2018		169,499,000
Beginning Balance at Dec. 31, 2018	12,111	$ 2	9,062	(423)	3,470
Stock-based compensation costs:
Net income	412
Ending Balance (shares) at Sep. 30, 2019		165,643,000
Ending Balance at Sep. 30, 2019	11,856	$ 2	9,142	(1,043)	3,755
Beginning Balance (shares) at Mar. 31, 2019		168,422,000
Beginning Balance at Mar. 31, 2019	12,209	$ 2	9,085	(644)	3,766
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Purchases of treasury stock (shares)		(1,349,000)
Purchases of treasury stock	(202)			(202)
Stock-based compensation costs:
Issued awards (shares)		49,000
Issued awards	0
Compensation costs included in net loss	38		38
Net income	(169)				(169)
Issued awards (shares)		49,000
Issued awards	0
Ending Balance (shares) at Jun. 30, 2019		167,122,000
Ending Balance at Jun. 30, 2019	11,876	$ 2	9,123	(846)	3,597
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared	(73)				(73)
Exercise of long-term incentive stock options		54,000
Exercise of employee stock purchases	6			6
Purchases of treasury stock (shares)		(1,619,000)
Purchases of treasury stock	(203)			(203)
Stock-based compensation costs:
Issued awards (shares)		86,000
Issued awards	0
Compensation costs included in net loss	19		19
Net income	231				231
Issued awards (shares)		86,000
Issued awards	0
Ending Balance (shares) at Sep. 30, 2019		165,643,000
Ending Balance at Sep. 30, 2019	11,856	$ 2	9,142	(1,043)	3,755
Beginning Balance (shares) at Dec. 31, 2019		165,547,000
Beginning Balance at Dec. 31, 2019	12,119	$ 2	9,161	(1,069)	4,025
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared	(91)				(91)
Exercise of long-term incentive stock options		8,000
Exercise of employee stock purchases	0		(1)	1
Purchases of treasury stock (shares)		(1,007,000)
Purchases of treasury stock	(122)			(122)
Stock-based compensation costs:
Issued awards (shares)		316,000
Issued awards	0
Compensation costs included in net loss	16		16
Net income	289				289
Issued awards (shares)		316,000
Issued awards	0
Ending Balance (shares) at Mar. 31, 2020		164,864,000
Ending Balance at Mar. 31, 2020	12,211	$ 2	9,176	(1,190)	4,223
Beginning Balance (shares) at Dec. 31, 2019		165,547,000
Beginning Balance at Dec. 31, 2019	$ 12,119	$ 2	9,161	(1,069)	4,025
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of long-term incentive stock options	7,728
Stock-based compensation costs:
Net income	$ (170)
Ending Balance (shares) at Sep. 30, 2020		164,403,000
Ending Balance at Sep. 30, 2020	11,654	$ 2	9,305	(1,235)	3,582
Beginning Balance (shares) at Mar. 31, 2020		164,864,000
Beginning Balance at Mar. 31, 2020	12,211	$ 2	9,176	(1,190)	4,223
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared	(91)				(91)
Equity component	230		230
Capped call	(113)		(113)
Deferred tax provision	(25)		(25)
Purchases of treasury stock (shares)		(592,000)
Purchases of treasury stock	(50)			(50)
Stock-based compensation costs:
Issued awards (shares)		4,000
Issued awards	0
Compensation costs included in net loss	17		17
Net income	(439)				(439)
Issued awards (shares)		4,000
Issued awards	0
Ending Balance (shares) at Jun. 30, 2020		164,276,000
Ending Balance at Jun. 30, 2020	11,740	$ 2	9,285	(1,240)	3,693
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared	(91)				(91)
Exercise of long-term incentive stock options		62,000
Exercise of employee stock purchases	6		(1)	7
Purchases of treasury stock (shares)		(19,000)
Purchases of treasury stock	(2)			(2)
Stock-based compensation costs:
Issued awards (shares)		84,000
Issued awards	0
Compensation costs included in net loss	21		21
Net income	(20)				(20)
Issued awards (shares)		84,000
Issued awards	0
Ending Balance (shares) at Sep. 30, 2020		164,403,000
Ending Balance at Sep. 30, 2020	$ 11,654	$ 2	$ 9,305	$ (1,235)	$ 3,582