Outstanding Exposure - Narrative (Details) € in Millions				1 Months Ended	12 Months Ended
		Jul. 31, 2015 USD ($)	Jul. 01, 2015 USD ($)	Aug. 31, 2014 line_of_credit	Dec. 31, 2015 USD ($)		Feb. 01, 2016 USD ($)	Jan. 18, 2016 USD ($)	Dec. 31, 2015 EUR (€)	Dec. 24, 2015 USD ($)	Sep. 09, 2015 USD ($)	Aug. 03, 2015 USD ($)	Dec. 31, 2014 USD ($)
Schedule of Insured Financial Obligations [Line Items]
Probability of paying more claims than being reimbursed (as a percent)					50.00%				50.00%
Net Debt Service Outstanding					$ 536,341,000,000								$ 609,622,000,000
Net Par Outstanding					358,571,000,000	[1],[2]							403,729,000,000	[3]
Indirect European exposure					4,200,000,000
Surety Reinsurance Contracts [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Debt Service Outstanding | €									€ 12
Pooled corporate obligations [Member]
Schedule of Insured Financial Obligations [Line Items]
Indirect European exposure					244,000,000
Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Debt Service Outstanding					41,915,000,000								56,010,000,000
Net Par Outstanding					37,128,000,000								50,247,000,000
Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Debt Service Outstanding					494,426,000,000								553,612,000,000
Net Par Outstanding					$ 321,443,000,000								353,482,000,000
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Maximum period of liquidity claims (in years)					1 year
Net Par Outstanding					$ 15,183,000,000								18,247,000,000
United Kingdom and Ireland [Member] | Mortgage Loans on Real Estate [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Debt Service Outstanding					102,000,000
United Kingdom and Ireland [Member] | Mortgage Loans on Real Estate [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Debt Service Outstanding													127,000,000
Select European Countries [Member]
Schedule of Insured Financial Obligations [Line Items]
Indirect European exposure					223,000,000
Greece [Member] | Pooled corporate obligations [Member]
Schedule of Insured Financial Obligations [Line Items]
Indirect European exposure					6,000,000
Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Debt Service Outstanding					8,597,000,000
Net Par Outstanding					5,053,000,000	[4]							4,939,000,000
Puerto Rico [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding					5,100,000,000
Commitment to Provide Guarantees [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Outstanding commitments to provide guaranties					595,000,000
Outstanding commitments to provide guaranties expiring prior to the date of filing					471,000,000
Outstanding commitments to provide guaranties, amount expiring prior to December 31, 2016					$ 60,000,000
Minimum [Member]
Schedule of Insured Financial Obligations [Line Items]
Constant discount rate (as a percent)					4.00%				4.00%
Minimum [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Expiration date for insured financial obligation commitments					Jan. 15, 2016
Minimum [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Constant discount rate (as a percent)					4.00%				4.00%
Maximum [Member]
Schedule of Insured Financial Obligations [Line Items]
Constant discount rate (as a percent)					5.00%				5.00%
Maximum [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Expiration date for insured financial obligation commitments					Feb. 25, 2017
Maximum [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Constant discount rate (as a percent)					5.00%				5.00%
PREPA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Percentage of outstanding bonds of PREPA				60.00%
Forbearance agreement, number of lines of credit with extended Maturity Dates | line_of_credit				2
Subject to the Terms of the Recovery Act [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Debt Service Outstanding					$ 4,540,000,000
Net Par Outstanding					2,575,000,000	[4]							2,447,000,000
Subject to the Terms of the Recovery Act [Member] | Puerto Rico Public Finance Corporation [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Missed debt service payment												$ 58,000,000
Subject to the Terms of the Recovery Act [Member] | Working Group For The Fiscal And Economic Recovery Of Puerto Rico [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Cumulative Financing Gap, Amount Before Corrective Action											$ 27,800,000,000
Cumulative Financing Gap, Net Of Corrective Action											$ 14,000,000,000
Subject to the Terms of the Recovery Act [Member] | PREPA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Bonds Issued in Settlement, Amount			$ 131,000,000
Subject to the Terms of the Recovery Act [Member] | PRHTA (Transportation revenue) [Member] | Maximum [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Special Assessment Bond, Potential Issuance Amount					2,950,000,000.00
Not Subject to the Terms of the Recovery Act [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Debt Service Outstanding					4,057,000,000
Net Par Outstanding					2,478,000,000	[4]							2,492,000,000
PRHTA (Transportation revenue) [Member] | Subject to the Terms of the Recovery Act [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	[5]				909,000,000	[4]							844,000,000
PREPA [Member] | Subject to the Terms of the Recovery Act [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding					744,000,000	[4]							772,000,000
Payments Received On Outstanding Principal Amounts			$ 416,000,000
PREPA [Member] | Subject to the Terms of the Recovery Act [Member] | AGM and AGC [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Bonds Bought In Settlement, Amount		$ 74,000,000
PRHTA (Highway revenue) [Member] | Subject to the Terms of the Recovery Act [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	[5]				370,000,000	[4]							273,000,000
Puerto Rico Municipal Finance Authority [Member] | Not Subject to the Terms of the Recovery Act [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding					387,000,000	[4]							$ 399,000,000
Radian [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding					10,900,000,000
Radian [Member] | Puerto Rico [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Increase in outstanding principal amount, due to acquisition, net					385,000,000
Radian [Member] | PREPA [Member] | Puerto Rico [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Increase in outstanding principal amount, due to acquisition, net					$ 21,000,000
Subsequent Event [Member] | Subject to the Terms of the Recovery Act [Member] | Working Group For The Fiscal And Economic Recovery Of Puerto Rico [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Cumulative Financing Gap, Amount Before Corrective Action								$ 63,400,000,000
Cumulative Financing Gap, Voluntary Exchange Of Tax Supported Debt, Amount							$ 49,200,000,000
Cumulative Financing Gap, Amount Proposed To Be Converted To Mandatorily Payable Base Bonds							26,500,000,000
Cumulative Financing Gap, Amount Proposed To Be Converted To Growth Bonds							$ 22,700,000,000
Surety Bond [Member] | PREPA [Member] | Restructuring Support Agreement [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Possible liquidity claims, gross exposure										$ 113,000,000
Bridge Loan [Member] | PREPA [Member] | Restructuring Support Agreement [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Guarantor Obligations, Debt Financing Amount										$ 15,000,000

[1] Excludes $1.5 billion of loss mitigation securities insured and held by the Company as of December 31, 2015, which are primarily BIG.

[2] The December 31, 2015 amounts include $10.9 billion of net par acquired from Radian Asset.

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

[4] As of December 31, 2015, the Company's Puerto Rico net exposures increased due to (1) net par of $385 million acquired in the Radian Asset Acquisition, of which $21 million was of PREPA and $166 million of PRHTA, and (2) a commutation of previously ceded Puerto Rico exposures.

[5] .