Income Taxes - Valuation Allowance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Valuation Allowance
Valuation allowance at beginning of period	$ 46	$ 177	$ 10,963
Valuation allowance at end of period	56	46	177
Income tax provision
Valuation Allowance
Increase (decrease) in valuation allowance	0	(9)	(975)
Other comprehensive income tax benefit (provision)
Valuation Allowance
Increase (decrease) in valuation allowance	24	(3)	(1,186)
Expirations
Valuation Allowance
Increase (decrease) in valuation allowance	(4)	(91)	0
Release of valuation allowance
Valuation Allowance
Increase (decrease) in valuation allowance	(10)	(28)	(8,310)
Other
Valuation Allowance
Increase (decrease) in valuation allowance	$ 0	$ 0	$ (315)