Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 335	$ (410)	$ 641	$ (4,511)
Other comprehensive (loss) income, net of taxes:
Unrealized gains on securities	1	1	2	1
Defined benefit plans:
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), Net of Tax	69	0	69	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), Tax	48		48
Amortization or curtailment of unrecognized amounts included in net periodic benefit costs	19	15	30	23
Foreign exchange losses	0	(1)	(1)	(10)
Other comprehensive income	89	15	100	14
Total comprehensive income (loss)	424	(395)	741	(4,497)
Total comprehensive income attributable to noncontrolling interests	(75)	(59)	(153)	(130)
Preferred dividends attributable to redeemable noncontrolling interest	0	(10)	0	(21)
Total comprehensive income (loss) attributable to common stockholders	$ 349	$ (464)	$ 588	$ (4,648)