CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Millions	Total	Subsidiary Equity Transactions [Member]	Equity Component Of Tangible Equity Units 1 [Member]	Common Stock [Member]	Paid-in Capital [Member]	Paid-in Capital [Member] Subsidiary Equity Transactions [Member]	Paid-in Capital [Member] Equity Component Of Tangible Equity Units 1 [Member]	Retained Earnings (Accumulated Deficit) [Member]	Retained Earnings (Accumulated Deficit) [Member] Subsidiary Equity Transactions [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Non- controlling Interests [Member]	Non- controlling Interests [Member] Subsidiary Equity Transactions [Member]	Non- controlling Interests [Member] Equity Component Of Tangible Equity Units 1 [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)	191							150				41
Common stock issued	6				6
Share-based compensation expense	84				84
Dividends—common stock	(254)							(254)
Repurchases of common stock	(1,973)				0					(1,973)
Subsidiary equity transactions		$ 5				$ (14)							$ 19
Settlement of tangible equity units			$ (70)				$ 230							$ (300)
Distributions to noncontrolling interest owners	(238)											(238)
Adjustments for pension and other postretirement plans	0
Other	1										1
Balance at Jun. 30, 2018	11,495			57	12,306			1,054		(4,105)	(410)	2,593
Balance at Mar. 31, 2018	11,756			57	11,701			1,152		(3,759)	(410)	3,015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	17							29				(12)
Common stock issued	6				6
Share-based compensation expense	45				45
Dividends—common stock	(127)							(127)
Repurchases of common stock	(14)				332					(346)
Subsidiary equity transactions		2				(8)			$ 0				10
Settlement of tangible equity units			$ (70)				$ 230							$ (300)
Distributions to noncontrolling interest owners	(120)											(120)
Adjustments for pension and other postretirement plans	0
Balance at Jun. 30, 2018	11,495			57	12,306			1,054		(4,105)	(410)	2,593
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)	(849)							(1,040)				191
Common stock issued	41			1	40
Share-based compensation expense	78				78
Dividends—common stock	(299)							(299)
Repurchases of common stock	(28)				0					(28)
Subsidiary equity transactions		(200)				624							(824)
Distributions to noncontrolling interest owners	(256)											(256)
Adjustments for pension and other postretirement plans	(45)										(45)
Other	1										1
Balance at Jun. 30, 2019	9,331			58	13,135			(149)		(4,892)	(379)	1,558
Balance at Mar. 31, 2019	10,533			57	13,057			1,024		(4,881)	(329)	1,605
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(945)							(1,025)				80
Common stock issued	41			1	40
Share-based compensation expense	40				40
Dividends—common stock	(149)							(149)
Repurchases of common stock	(11)									(11)
Subsidiary equity transactions		$ (2)				$ (2)			$ 1				$ (1)
Distributions to noncontrolling interest owners	(126)											(126)
Adjustments for pension and other postretirement plans	(50)										(50)
Balance at Jun. 30, 2019	$ 9,331			$ 58	$ 13,135			$ (149)		$ (4,892)	$ (379)	$ 1,558