Income Taxes - Valuation Allowance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Valuation Allowance
Valuation allowance at beginning of period	$ 56	$ 46	$ 177
Valuation allowance at end of period	40	56	46
Income tax provision
Valuation Allowance
Increase (decrease) in valuation allowance	0	0	(9)
Other comprehensive income tax (provision) benefit
Valuation Allowance
Increase (decrease) in valuation allowance	(16)	24	(3)
Expirations
Valuation Allowance
Increase (decrease) in valuation allowance	0	(4)	(91)
Release of valuation allowance
Valuation Allowance
Increase (decrease) in valuation allowance	$ 0	$ (10)	$ (28)