Pension and Other Postretirement Benefits-Post Retirement Benefit Cost (Details) - Other Postretirement Benefit Plan, Defined Benefit [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	$ 1	$ 1	$ 3	$ 3
Amortization of reduction in liability resulting from plan amendment	(1)	(2)	(4)	(5)
Gain from curtailment	0	0	(13)	0	$ (46)
Amortization of net actuarial gain	(1)	0	(1)	0
Net periodic postretirement benefit cost	$ (1)	$ (1)	$ (15)	$ (2)