Income Taxes - Valuation Allowance (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Valuation Allowance [Line Items]
Valuation allowance at beginning of period				$ 10,705
Valuation allowance at end of period	46	177	10,963	10,705
Income tax provision
Valuation Allowance [Line Items]
Increase (decrease) in valuation allowance	(9)	(975)	(432)
Other comprehensive income tax benefit
Valuation Allowance [Line Items]
Increase (decrease) in valuation allowance	(3)	(1,186)	690
Expirations
Valuation Allowance [Line Items]
Increase (decrease) in valuation allowance	(91)	0	0
Release of valuation allowance
Valuation Allowance [Line Items]
Increase (decrease) in valuation allowance	(28)	(8,310)	0
Other
Valuation Allowance [Line Items]
Increase (decrease) in valuation allowance	$ 0	$ (315)	$ 0