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]	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]	Noncontrolling Interests [Member] Equity Component of 7.5% Tangible Equity Units [Member]
Balance at Dec. 31, 2012	$ 21,882			$ 51	$ 8,230		$ 13,829		$ (841)	$ (640)	$ 1,253
Net income (loss)	941						801				140
Common stock issued	293			1	292
Dividends—common stock	(274)						(274)
Repurchase of common stock	(54)								(54)
Subsidiary equity transaction		$ 661				$ 107						$ 554
Distributions to noncontrolling interest owners	(156)										(156)
Contributions from noncontrolling interest owners	2										2
Reclassification of previously deferred derivative losses to (gains) losses on derivatives, net	7									7
Adjustments for pension and other postretirement plans	348									348
Balance at Dec. 31, 2013	23,650			52	8,629		14,356		(895)	(285)	1,793
Net income (loss)	(1,563)						(1,750)				187
Common stock issued	286				286
Dividends—common stock	(505)						(505)
Repurchase of common stock	(45)								(45)
Subsidiary equity transaction		943				90		$ 24				829
Distributions to noncontrolling interest owners	(216)										(216)
Reclassification of previously deferred derivative losses to (gains) losses on derivatives, net	6									6
Adjustments for pension and other postretirement plans	(238)									(238)
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	209				209
Dividends—common stock	(553)						(553)
Repurchase of common stock	(55)								(55)
Subsidiary equity transaction		$ 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