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, 2016	Mar. 31, 2015
Before-Tax Amount
Amortization of prior service cost included in net periodic pension and postretirement cost	$ 0	$ (1)
Amortization of actuarial loss included in net periodic pension and postretirement cost	5	5
Other comprehensive income – pension benefits	5	4
Tax Benefit
Amortization of prior service cost included in net periodic pension and postretirement cost	0	0
Amortization of actuarial loss included in net periodic pension and postretirement cost	(1)	(1)
Other comprehensive income – pension benefits	(1)	(1)
Net-of-Tax Amount
Amortization of prior service cost included in net periodic pension and postretirement cost	0	(1)
Amortization of actuarial loss included in net periodic pension and postretirement cost	4	4
Other comprehensive income – pension benefits	$ 4	$ 3