Employee Benefit Plans - Postretirement (Details) - Other Postretirement Benefit Plan, Defined Benefit [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Interest Cost	$ 0	$ 1	$ 0	$ 1
Amortization of prior service cost	(1)	(1)	(4)	(4)
Actuarial loss	0	0	1	1
Net benefit cost	$ (1)	$ 0	$ (3)	$ (2)