Outstanding Exposure - Net Direct Economic Exposure to Selected European Countries (Details) $ in Millions	Sep. 30, 2016 USD ($)	[1]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	$ 2,463
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	806
Hungary [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	432
Hungary [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	360
Italy [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	1,382
Italy [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	0
Portugal [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	80
Portugal [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	80
Spain [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	366
Spain [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	366
Turkey [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	203
Turkey [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	0
Total Sovereign Exposure [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	1,653	[2]
Total Sovereign Exposure [Member] | Hungary [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	252	[2]
Total Sovereign Exposure [Member] | Italy [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	955	[2]
Total Sovereign Exposure [Member] | Portugal [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	80	[2]
Total Sovereign Exposure [Member] | Spain [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	366	[2]
Total Sovereign Exposure [Member] | Turkey [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	0	[2]
Total Non-sovereign Exposure [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	810	[3]
Total Non-sovereign Exposure [Member] | Hungary [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	180	[3]
Total Non-sovereign Exposure [Member] | Italy [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	427	[3]
Total Non-sovereign Exposure [Member] | Portugal [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	0	[3]
Total Non-sovereign Exposure [Member] | Spain [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	0	[3]
Total Non-sovereign Exposure [Member] | Turkey [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure	$ 203	[3]

[1] While the Company’s exposures are shown in U.S. dollars, the obligations the Company insures are in various currencies, primarily Euros.

[2] Sub-sovereign exposure in Selected European Countries includes transactions backed by receivables from or supported by sub-sovereigns, which are governmental or government-backed entities other than the ultimate governing body of the country.

[3] Non-sovereign exposure in Selected European Countries includes debt of regulated utilities, RMBS and diversified payment rights ("DPR") securitizations.