CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 2,095	$ (4,025)	$ (12,089)
Other comprehensive income (loss), net of taxes:
Unrealized gains on securities	1	2	0
Defined benefit plans:
Actuarial gains (losses) arising during the period, net of taxes	(14)	88	5
Amortization or curtailment of unrecognized amounts included in net periodic benefit costs	54	44	38
Foreign exchange (losses) gains	0	(1)	8
Other comprehensive income (loss)	69	(43)	41
Total comprehensive income (loss)	2,164	(4,068)	(12,048)
Total comprehensive income attributable to noncontrolling interests	(286)	(292)	(106)
Gain on redemption and preferred dividends attributable to noncontrolling interests	0	161	(41)
Total comprehensive income (loss) attributable to common stockholders	$ 1,878	$ (4,199)	$ (12,195)