Income Taxes (Provision) (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Income Tax Expense (Benefit), Continuing Operations [Abstract]
Income before income taxes	$ 60	$ 39	[1]	$ 162	$ 88	[1]
Income tax expense	$ 11	$ 8	[1]	$ 17	$ 15	[1]
Effective income tax rate	18.30%	20.50%		10.50%	17.00%
U.S. federal statutory rate (as a percent)				21.00%	35.00%

[1] (a) Retrospectively adjusted as discussed in Note 1, Nature of Business.