Employee Benefit Plans (Details) - Other Postretirement Benefit Plans, Defined Benefit [Member] - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Interest cost on accumulated benefit obligation		$ 1	$ 1	$ 2	$ 2
Amortization of prior service cost		1	0	1	0
Net periodic cost (1)	[1]	2	$ 1	3	$ 2
Contribution expected in 2017				5
Contribution made in period		$ 1		$ 3

[1] Net periodic cost in this table is before considering amounts subject to overhead allocations for capital expenditure projects or for amounts subject to deferral for regulatory purposes.