CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 2,894	$ 2,095	$ (4,025)
Other comprehensive income (loss), net of taxes:
Unrealized gains on securities	0	1	2
Defined benefit plans:
Actuarial (losses) gains arising during the period, net of taxes	77	(14)	88
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	4	0	0
Amortization or curtailment of unrecognized amounts included in net periodic benefit costs	48	54	44
Foreign exchange losses	(1)	0	(1)
Other comprehensive (loss) income	(34)	69	(43)
Total comprehensive income (loss)	2,860	2,164	(4,068)
Total comprehensive income attributable to noncontrolling interests	(291)	(286)	(292)
Gain on redemption and preferred dividends attributable to noncontrolling interests	0	0	161
Total comprehensive income (loss) attributable to common stockholders	$ 2,569	$ 1,878	$ (4,199)