Outstanding Exposure - BIG Net Par Outstanding (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, Credit Derivative	$ 31,731		$ 34,996
Net Par Outstanding (excluding loss mitigation bonds)	389,099.0	[1]	403,729.0	[2]
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, Financial Guaranty Insurance	14,937	[3]	15,222	[3]
Net Par Outstanding, Credit Derivative	2,923		3,025
Net Par Outstanding (excluding loss mitigation bonds)	17,860.0		18,247.0
Number of Risks, Financial Guaranty Insurance	356	[3],[4]	358	[3],[4]
Number of Risks, Credit Derivative	55	[4]	56	[4]
Number of Risks	411	[4]	414	[4]
BIG [Member] | BIG 1 [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, Financial Guaranty Insurance	9,887	[3]	10,195	[3]
Net Par Outstanding, Credit Derivative	1,451		1,670
Net Par Outstanding (excluding loss mitigation bonds)	11,338.0		11,865.0
Number of Risks, Financial Guaranty Insurance	164	[3],[4]	164	[3],[4]
Number of Risks, Credit Derivative	18	[4]	18	[4]
Number of Risks	182	[4]	182	[4]
BIG [Member] | BIG 2 [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, Financial Guaranty Insurance	2,345	[3]	2,135	[3]
Net Par Outstanding, Credit Derivative	684		554
Net Par Outstanding (excluding loss mitigation bonds)	3,029.0		2,689.0
Number of Risks, Financial Guaranty Insurance	73	[3],[4]	75	[3],[4]
Number of Risks, Credit Derivative	12	[4]	14	[4]
Number of Risks	85	[4]	89	[4]
BIG [Member] | BIG 3 [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, Financial Guaranty Insurance	2,705	[3]	2,892	[3]
Net Par Outstanding, Credit Derivative	788		801
Net Par Outstanding (excluding loss mitigation bonds)	$ 3,493.0		$ 3,693.0
Number of Risks, Financial Guaranty Insurance	119	[3],[4]	119	[3],[4]
Number of Risks, Credit Derivative	25	[4]	24	[4]
Number of Risks	144	[4]	143	[4]

[1] Excludes $1.3 billion of loss mitigation securities insured and held by the Company as of March 31, 2015, which are primarily in the BIG category.

[2] Excludes $1.3 billion of loss mitigation securities insured and held by the Company as of December 31, 2014, which are primarily in the BIG category.

[3] Includes net par outstanding for FG VIEs.

[4] A risk represents the aggregate of the financial guaranty policies that share the same revenue source for purposes of making Debt Service payments.