Financial Guaranty Insurance Premiums - Gross Premium Receivable Net of Commissions on Assumed Business Roll Forward (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Effects of Reinsurance [Line Items]
Non-financial guaranty line of business	$ 1
Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member]
Gross Premium Receivable Net of Ceding Commissions [Roll Forward]
Beginning of period, December 31	729		876		876
Gross premium written, net of commissions on assumed business	36		33
Gross premiums received, net of commissions on assumed business	(36)		(53)
Changes in the expected term	(6)		(3)
Accretion of discount, net of commissions on assumed business	5		7
Foreign exchange translation	(25)		2
Consolidation/deconsolidation of FG VIEs	(4)		1
Other adjustments	0		0
End of period, March 31	699	[1]	863	[1]
Variable Interest Entity, Primary Beneficiary [Member]
Gross Premium Receivable Net of Ceding Commissions [Roll Forward]
End of period, March 31	$ 22		$ 18
Foreign Currency Concentration Risk [Member] | Premiums Receivable [Member]
Gross Premium Receivable Net of Ceding Commissions [Roll Forward]
Percentage of installment premiums denominated in currencies other than the U.S. dollar	49.00%				51.00%

[1] Excludes $22 million and $18 million as of March 31, 2015 and March 31, 2014, respectively, related to consolidated FG VIEs.