Pension and Other Postretirement Benefits-Post Retirement Benefit Cost (Details) - Other Postretirement Benefit Plan, Defined Benefit [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	$ 1	$ 1	$ 2	$ 2
Amortization of reduction in liability resulting from plan amendment	(1)	(1)	(3)	(3)
Gain from curtailment	(13)	0	(13)	0	$ (46)
Net periodic postretirement benefit cost	$ (13)	$ 0	$ (14)	$ (1)