Outstanding Exposure - Net Direct Economic Exposure to Selected European Countries (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	$ 2,353	[1]
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	900	[1]
Hungary [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	499	[1]
Hungary [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	424	[1]
Italy [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	1,378	[1]
Italy [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	0	[1]
Portugal [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	102	[1]
Portugal [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	102	[1]
Spain [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	374	[1]
Spain [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	374	[1]
Total Sovereign Exposure [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	1,680	[1]
Total Sovereign Exposure [Member] | Non-Infrastructure Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	1,208	[1],[2]
Total Sovereign Exposure [Member] | Infrastructure finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	472	[1]
Total Sovereign Exposure [Member] | Hungary [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	313	[1]
Total Sovereign Exposure [Member] | Hungary [Member] | Non-Infrastructure Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	0	[1],[2]
Total Sovereign Exposure [Member] | Hungary [Member] | Infrastructure finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	313	[1]
Total Sovereign Exposure [Member] | Italy [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	891	[1]
Total Sovereign Exposure [Member] | Italy [Member] | Non-Infrastructure Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	878	[1],[2]
Total Sovereign Exposure [Member] | Italy [Member] | Infrastructure finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	13	[1]
Total Sovereign Exposure [Member] | Portugal [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	102	[1]
Total Sovereign Exposure [Member] | Portugal [Member] | Non-Infrastructure Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	91	[1],[2]
Total Sovereign Exposure [Member] | Portugal [Member] | Infrastructure finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	11	[1]
Total Sovereign Exposure [Member] | Spain [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	374	[1]
Total Sovereign Exposure [Member] | Spain [Member] | Non-Infrastructure Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	239	[1],[2]
Total Sovereign Exposure [Member] | Spain [Member] | Infrastructure finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	135	[1]
Total Non-sovereign Exposure [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	673	[1]
Total Non-sovereign Exposure [Member] | Regulated utilities [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	220	[1]
Total Non-sovereign Exposure [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	453	[1]
Total Non-sovereign Exposure [Member] | Hungary [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	186	[1]
Total Non-sovereign Exposure [Member] | Hungary [Member] | Regulated utilities [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	0	[1]
Total Non-sovereign Exposure [Member] | Hungary [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	186	[1]
Total Non-sovereign Exposure [Member] | Italy [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	487	[1]
Total Non-sovereign Exposure [Member] | Italy [Member] | Regulated utilities [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	220	[1]
Total Non-sovereign Exposure [Member] | Italy [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	267	[1]
Total Non-sovereign Exposure [Member] | Portugal [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	0	[1]
Total Non-sovereign Exposure [Member] | Portugal [Member] | Regulated utilities [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	0	[1]
Total Non-sovereign Exposure [Member] | Portugal [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	0	[1]
Total Non-sovereign Exposure [Member] | Spain [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	0	[1]
Total Non-sovereign Exposure [Member] | Spain [Member] | Regulated utilities [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	0	[1]
Total Non-sovereign Exposure [Member] | Spain [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	$ 0	[1]

[1] (1)While the Company’s exposures are shown in U.S. dollars, the obligations the Company insures are in various currencies, primarily Euros. One of the residential mortgage-backed securities included in the table above includes residential mortgages in both Italy and Germany, and only the portion of the transaction equal to the portion of the original mortgage pool in Italian mortgages is shown in the table.

[2] (2)The exposure shown in the “Non-infrastructure public finance” category is from transactions backed by receivable payments from sub-sovereigns in Italy, Spain and Portugal. Sub-sovereign debt is debt issued by a governmental entity or government backed entity, or supported by such an entity, that is other than direct sovereign debt of the ultimate governing body of the country.