CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net Income (Loss)	$ (211)	$ (2,808)	$ (6,812)
Adjustments for derivative instruments
Reclassification of previously deferred derivative losses to (gains) losses on derivatives, net	3	8	10
Income taxes on reclassification of previously deferred derivative losses to (gains) losses on derivatives, net	(1)	(3)	(4)
Total adjustments for derivative instruments, net of taxes	2	5	6
Adjustments for pension and other postretirement plans
Net gain (loss) incurred during period	(14)	(175)	49
Income taxes on net gain (loss) incurred during period	4	68	(18)
Prior service credit (cost) incurred during period	0	0	89
Income taxes on prior service credit (cost) incurred during period	0	0	(33)
Amortization of net actuarial (gain) loss to general and administrative expense	116	188	63
Income taxes on amortization of net actuarial (gain) loss to general and administrative expense	(40)	(73)	(20)
Amortization of net prior service (credit) cost to general and administrative expense	(25)	(34)	(4)
Income taxes on amortization of net prior service (credit) cost to general and administrative expense	10	13	2
Total adjustments for pension and other postretirement plans, net of taxes	51	(13)	128
Total	53	(8)	134
Comprehensive Income (Loss)	(158)	(2,816)	(6,678)
Comprehensive income (loss) attributable to noncontrolling interests	245	263	(120)
Comprehensive Income (Loss) Attributable to Common Stockholders	$ (403)	$ (3,079)	$ (6,558)