Reinsurance and Other Monoline Exposures - Narrative (Details) - USD ($)		9 Months Ended		12 Months Ended
	Jan. 01, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Ceded Credit Risk [Line Items]
Reassumed ceded business, par due to commutations			$ 856,000,000
Fixed-maturity securities		$ 11,162,000,000		$ 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		72,000,000
AGC [Member]
Ceded Credit Risk [Line Items]
Amounts could be required to pay if third party exercised right to recapture business		37,000,000
Fixed Maturities [Member]
Ceded Credit Risk [Line Items]
Fixed-maturity securities		10,640,000,000		10,491,000,000
Fixed Maturities [Member] | National Public Finance Guarantee Corporation [Member]
Ceded Credit Risk [Line Items]
Fixed-maturity securities		258,000,000
Fixed Maturities [Member] | Ambac [Member]
Ceded Credit Risk [Line Items]
Fixed-maturity securities		217,000,000
Fixed Maturities [Member] | Other [Member]
Ceded Credit Risk [Line Items]
Fixed-maturity securities		31,000,000
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