Income Taxes (Provision) (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016		Sep. 30, 2017	Sep. 30, 2016
Income Tax Expense (Benefit), Continuing Operations [Abstract]
Income before income taxes	$ 49	$ 63	[1]	$ 100	$ 141	[1]
Income tax expense	$ 8	$ 13	[1]	$ 15	$ 25	[1]
Effective income tax rate	16.30%	20.60%		15.00%	17.70%
U.S. federal statutory rate (as a percent)				35.00%

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