Reinsurance and Other Monoline Exposures - Narrative (Details) (USD $)	3 Months Ended		0 Months Ended	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2015	Jan. 01, 2014	Dec. 31, 2014
Ceded Credit Risk [Line Items]
Reassumed ceded business, par due to commutations	$ 856,000,000
Fixed-maturity securities		10,182,000,000		11,258,000,000
Assured Guaranty Re [Member]
Ceded Credit Risk [Line Items]
Amounts could be required to pay if third party exercised right to recapture business		81,000,000
AGC [Member]
Ceded Credit Risk [Line Items]
Amounts could be required to pay if third party exercised right to recapture business		48,000,000
Fixed Maturities [Member]
Ceded Credit Risk [Line Items]
Fixed-maturity securities		9,833,000,000		10,491,000,000
Fixed Maturities [Member] | National Public Finance Guarantee Corporation [Member]
Ceded Credit Risk [Line Items]
Fixed-maturity securities		291,000,000
Fixed Maturities [Member] | Ambac [Member]
Ceded Credit Risk [Line Items]
Fixed-maturity securities		247,000,000
Fixed Maturities [Member] | Other [Member]
Ceded Credit Risk [Line Items]
Fixed-maturity securities		32,000,000
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		$ 19,000,000