Employee Benefit Plans - Postretirement Plan (Details) - Postretirement Plan - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service benefit	$ (2)	$ (1)	$ (4)	$ (4)
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	(1)	0	(1)	(1)
Net periodic benefit cost (income)	$ (1)	$ (1)	$ (3)	$ (3)