CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net Income (Loss)	$ 17	$ (334)	$ 191	$ (609)
Adjustments for derivative instruments
Reclassification of previously deferred derivative losses to (gains) losses on derivatives, net	0	1	1	2
Income taxes on reclassification of previously deferred derivative losses	0	(1)	0	(1)
Total adjustments for derivative instruments, net of taxes	0	0	1	1
Adjustments for pension and other postretirement plans
Net gain (loss) incurred during period	0	19	0	15
Income taxes on net gain (loss) incurred during period	0	(6)	0	(5)
Amortization of net actuarial (gain) loss to other (income) expense, net	6	62	13	71
Income taxes on amortization of net actuarial (gain) loss	(1)	(23)	(3)	(26)
Amortization of net prior service (credit) cost to other (income) expense, net	(6)	(6)	(12)	(12)
Income taxes on amortization of net prior service (credit) cost	1	2	2	4
Total adjustments for pension and other postretirement plans, net of taxes	0	48	0	47
Total	0	48	1	48
Comprehensive Income (Loss)	17	(286)	192	(561)
Comprehensive income (loss) attributable to noncontrolling interests	(12)	81	41	124
Comprehensive Income (Loss) Attributable to Common Stockholders	$ 29	$ (367)	$ 151	$ (685)