CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Millions	Total	Subsidiary Equity Transactions [Member]	Common Stock [Member]	Paid-in Capital [Member]	Paid-in Capital [Member] Subsidiary Equity Transactions [Member]	Retained Earnings [Member]	Retained Earnings [Member] Subsidiary Equity Transactions [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interests [Member]	Noncontrolling Interests [Member] Subsidiary Equity Transactions [Member]
Balance at Dec. 31, 2017	$ 13,790		$ 57	$ 12,000		$ 1,109		$ (2,132)	$ (338)	$ 3,094
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	174					121				53
Share-based compensation expense	39			39
Dividends—common stock	(127)					(127)
Repurchases of common stock	(1,959)			(332)				(1,627)
Subsidiary equity transactions		$ 3			$ (6)						$ 9
Distributions to noncontrolling interest owners	(118)									(118)
Adjustments for pension and other postretirement plans	0
Other	1								1
Balance at Mar. 31, 2018	11,756		57	11,701		1,152		(3,759)	(410)	3,015
Balance at Dec. 31, 2018	10,943		57	12,393		1,245		(4,864)	(335)	2,447
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	96					(15)				111
Share-based compensation expense	38			38
Dividends—common stock	(150)					(150)
Repurchases of common stock	(17)							(17)
Subsidiary equity transactions		$ (198)			$ 626		$ (1)				$ (823)
Distributions to noncontrolling interest owners	(130)									(130)
Adjustments for pension and other postretirement plans	5								5
Other	1								1
Balance at Mar. 31, 2019	$ 10,533		$ 57	$ 13,057		$ 1,024		$ (4,881)	$ (329)	$ 1,605