Income Taxes - Unrecognized Tax Benefits (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2015
Income Tax Contingency [Line Items]
Unrecognized tax benefits as of December 31	$ 213,000,000	$ 514,000,000	$ 648,000,000
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0	0	0
Unrecognized Tax Benefit Resulting in Tax Credits and/or Net Operating Loss Carryforward	91,000,000	220,000,000	648,000,000
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of January 1	514,000,000	648,000,000	758,000,000
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	(301,000,000)	(134,000,000)	(110,000,000)
Unrecognized tax benefits as of December 31	213,000,000	514,000,000	648,000,000
Scenario, Forecast [Member]
Income Tax Contingency [Line Items]
Settlements				$ (213,000,000)