Reinsurance and Other Monoline Exposures - Narrative (Details) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 24, 2012	Jan. 01, 2014
Ceded Credit Risk [Line Items]
Fixed-maturity securities	$ 11,258,000,000	$ 10,615,000,000
Commutation gains recorded in other income	23,000,000	2,000,000	82,000,000
Non-affiliated Reinsurers [Member]
Ceded Credit Risk [Line Items]
Collateral posted by non-affiliated reinsurers	610,000,000
Radian [Member]
Ceded Credit Risk [Line Items]
Approximate amount of insurance risk agreed to be assumed				1,800,000,000
Payment Received for Assumed Insured Risk				22,000,000
Assured Guaranty Re [Member]
Ceded Credit Risk [Line Items]
Amounts could be required to pay if third party exercised right to recapture business	85,000,000
AGC [Member]
Ceded Credit Risk [Line Items]
Amounts could be required to pay if third party exercised right to recapture business	45,000,000
Fixed Maturities [Member]
Ceded Credit Risk [Line Items]
Fixed-maturity securities	10,491,000,000	9,711,000,000
Fixed Maturities [Member] | National Public Finance Guarantee Corporation [Member]
Ceded Credit Risk [Line Items]
Fixed-maturity securities	330,000,000
Fixed Maturities [Member] | Ambac [Member]
Ceded Credit Risk [Line Items]
Fixed-maturity securities	266,000,000
Fixed Maturities [Member] | Other [Member]
Ceded Credit Risk [Line Items]
Fixed-maturity securities	29,000,000
Excess of Loss Reinsurance Facility [Member] | AGM, AGC and MAC [Member]
Ceded Credit Risk [Line Items]
Minimum net losses required for attachment of excess of loss reinsurance facility					1,500,000,000
Amount of losses covered under the facility					500,000,000
Reinsurance retention policy, excess retention, amount reinsured					450,000,000
Remaining amount of losses covered under the facility					50,000,000
Premiums paid during the period	19,000,000
Remaining insurance premium payable	$ 19,000,000