CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net Income (Loss)	$ (6,812)	$ (1,563)	$ 941
Adjustments for derivative instruments
Reclassification of previously deferred derivative losses to (gains) losses on derivatives, net	10	9	11
Income taxes on reclassification of previously deferred derivative losses to (gains) losses on derivatives, net	(4)	(3)	(4)
Total adjustments for derivative instruments, net of taxes	6	6	7
Adjustments for pension and other postretirement plans
Net gain (loss) incurred during period	49	(405)	416
Income taxes on net gain (loss) incurred during period	(18)	149	(152)
Prior service credit (cost) incurred during period	89	0	0
Income taxes on prior service credit (cost) incurred during period	(33)	0	0
Amortization of net actuarial (gain) loss to general and administrative expense	63	27	132
Income taxes on amortization of net actuarial (gain) loss to general and administrative expense	(20)	(9)	(49)
Amortization of net prior service (credit) cost to general and administrative expense	(4)	0	1
Income taxes on amortization of net prior service (credit) cost to general and administrative expense	2	0	0
Total adjustments for pension and other postretirement plans, net of taxes	128	(238)	348
Total	134	(232)	355
Comprehensive Income (Loss)	(6,678)	(1,795)	1,296
Comprehensive income (loss) attributable to noncontrolling interests	(120)	187	140
Comprehensive Income (Loss) Attributable to Common Stockholders	$ (6,558)	$ (1,982)	$ 1,156