Benefit Plans - Net Periodic Benefit Costs (Details) - Nonqualified plan - Pension plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Periodic Benefit Costs [Abstract]
Interest cost	$ 3	$ 4	$ 4
Amortization of prior service cost (credit)	(1)	(1)	(1)
Net (gain) loss recognition	(4)	1	1
Net periodic benefit cost	$ (2)	$ 4	$ 4