CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Millions	Total	Subsidiary Equity Transactions [Member]	Equity Component of 7.5% Tangible Equity Units [Member]	Common Stock [Member]	Paid-in Capital [Member]	Paid-in Capital [Member] Subsidiary Equity Transactions [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interests [Member]	Noncontrolling Interests [Member] Subsidiary Equity Transactions [Member]	Noncontrolling Interests [Member] Equity Component of 7.5% Tangible Equity Units [Member]
Balance at Dec. 31, 2014	$ 22,318			$ 52	$ 9,005		$ 12,125	$ (940)	$ (517)	$ 2,593
Net income (loss)	(6,812)						(6,692)			(120)
Common stock issued	31			0	31		0	0
Share-based compensation expense	178				178
Dividends—common stock	(553)						(553)
Repurchase of common stock	(55)							(55)
Subsidiary equity transactions		$ 150	$ 348			$ 51					$ 99	$ 348
Distributions to noncontrolling interest owners	(282)									(282)
Reclassification of previously deferred derivative losses to (gains) losses on derivatives, net	6								6
Adjustments for pension and other postretirement plans	128								128
Balance at Dec. 31, 2015	15,457			52	9,265		4,880	(995)	(383)	2,638
Net income (loss)	(2,808)						(3,071)			263
Common stock issued	2,155			5	2,150		0	0
Share-based compensation expense	197				197
Dividends—common stock	(105)						(105)
Repurchase of common stock	(38)							(38)
Subsidiary equity transactions		1,009				263					746
Distributions to noncontrolling interest owners	(362)									(362)
Reclassification of previously deferred derivative losses to (gains) losses on derivatives, net	5								5
Adjustments for pension and other postretirement plans	(13)								(13)
Balance at Dec. 31, 2016	15,497			57	11,875		1,704	(1,033)	(391)	3,285
Net income (loss)	(211)						(456)			245
Share-based compensation expense	163				163
Dividends—common stock	(111)						(111)
Repurchase of common stock	(1,099)							(1,099)
Subsidiary equity transactions		$ (26)				$ (35)					$ 9
Distributions to noncontrolling interest owners	(445)									(445)
Reclassification of previously deferred derivative losses to (gains) losses on derivatives, net	2								2
Adjustments for pension and other postretirement plans	51								51
Balance at Dec. 31, 2017	13,790			$ 57	12,000		1,109	$ (2,132)	$ (338)	$ 3,094
Cumulative effect of accounting change	$ (31)				$ (3)		$ (28)