Pension Plans, Postretirement and Other Employee Benefits - Amounts Recognized for Pension and Postretirement Benefits in Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Before-Tax Amount
Amortization of actuarial loss included in net periodic pension and postretirement cost	$ 4	$ 5
Settlement Charge	6	0
Other comprehensive income – pension benefits	10	5
Tax Benefit
Amortization of actuarial loss included in net periodic pension and postretirement cost	(1)	(1)
Settlement Charge	(2)	0
Other comprehensive income – pension benefits	(3)	(1)
Net-of-Tax Amount
Amortization of actuarial loss included in net periodic pension and postretirement cost	3	4
Settlement Charge	4	0
Other comprehensive income – pension benefits	$ 7	$ 4