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 long-term incentive stock options and 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
Ending Balance (shares) at Mar. 31, 2019		168,422,000
Ending Balance at Mar. 31, 2019	12,209	$ 2	9,085	(644)	3,766
Stock-based compensation costs:
Purchases of treasury stock (shares)		1,594,000
Purchases of treasury stock	222			222
Issued awards (shares)		507,000
Issued awards	$ 0
Dividends declared per share	$ 0.32
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	7,728	8,000
Exercise of long-term incentive stock options and 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
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
Stock-based compensation costs:
Purchases of treasury stock (shares)		1,007,000
Purchases of treasury stock	122			$ 122
Issued awards (shares)		316,000
Issued awards	$ 0
Dividends declared per share	$ 0.55