Outstanding Exposure - Narrative (Details) - USD ($)			6 Months Ended
		Jul. 01, 2016	Jun. 30, 2016		Mar. 04, 2016	Dec. 31, 2015		Dec. 24, 2015	Sep. 15, 2015
Schedule of Insured Financial Obligations [Line Items]
Net Debt Service Outstanding			$ 488,362,000,000			$ 536,341,000,000
Indirect European exposure			3,500,000,000
Net par amount outstanding			329,864,000,000	[1]		358,571,000,000	[2]
Net Par Outstanding, European Exposure	[3]		2,314,000,000
Pooled corporate obligations [Member]
Schedule of Insured Financial Obligations [Line Items]
Indirect European exposure			192,000,000
Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Debt Service Outstanding			33,306,000,000			41,915,000,000
Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Debt Service Outstanding			455,056,000,000			494,426,000,000
Diversified Payment Rights [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, European Exposure			$ 204,000,000
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Maximum period of liquidity claims (in years)			1 year
Net par amount outstanding			$ 14,790,000,000			15,183,000,000
Net Par Outstanding, European Exposure	[3]		815,000,000
AAA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding			16,061,000,000			20,837,000,000
Ireland [Member] | Mortgage Loans on Real Estate [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Debt Service Outstanding			104,000,000			102,000,000
United States [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding			6,082,000,000			7,067,000,000
United States [Member] | Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding			25,562,000,000	[1]		31,770,000,000	[2]
United States [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding			272,114,000,000	[1],[4]		291,866,000,000	[2]
United States [Member] | BIG [Member] | RMBS [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding			3,427,000,000			3,973,000,000
United States [Member] | BIG [Member] | Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding			4,553,000,000			5,469,000,000
United States [Member] | BIG [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding			8,268,000,000	[4]		7,784,000,000
United States [Member] | AAA [Member] | Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding			11,362,000,000			14,366,000,000
United States [Member] | AAA [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding			2,376,000,000			3,053,000,000
Select European Countries [Member]
Schedule of Insured Financial Obligations [Line Items]
Indirect European exposure			203,000,000
Greece [Member] | Pooled corporate obligations [Member]
Schedule of Insured Financial Obligations [Line Items]
Indirect European exposure			4,000,000
Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Debt Service Outstanding			8,466,000,000
Net par amount outstanding			5,054,000,000			$ 5,053,000,000
Puerto Rico [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount 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			117,000,000
Commitments due before expiration date			$ 53,000,000
Minimum [Member]
Schedule of Insured Financial Obligations [Line Items]
Probability of paying more claims than being reimbursed (as a percent)			50.00%
Minimum [Member] | Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Expiration date for insured financial obligation commitments			Jul. 01, 2016
Minimum [Member] | BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Constant discount rate (as a percent)			4.00%
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%
PRHTA (Highway revenue) [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Obligations secured by taxes on crude oil, unfinished oil and derivative products			$ 120,000,000
PREPA [Member] | AGM and AGC [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Payment On Outstanding Principal Amount			$ 74,000,000
Puerto Rico Aqueduct and Sewer Authority [Member] | U.S. Justice Department and U.S. Environmental Protection Agency [Member]
Schedule of Insured Financial Obligations [Line Items]
Settlement agreement, required spending threshold									$ 1,600,000,000
Settlement agreement, required spending, payable to contractor					$ 140,000,000
Surety Bond [Member] | Restructuring Support Agreement [Member] | PREPA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Possible liquidity claims, gross exposure								$ 113,000,000
Surety Bond [Member] | AGC [Member] | Restructuring Support Agreement [Member] | PREPA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Possible liquidity claims, gross exposure								14,000,000
Surety Bond [Member] | AGM [Member] | Restructuring Support Agreement [Member] | PREPA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Possible liquidity claims, gross exposure								99,000,000
Bridge Loan [Member] | Restructuring Support Agreement [Member] | PREPA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Guarantor obligations, debt financing amount								15,000,000
Bridge Loan [Member] | AGC [Member] | Restructuring Support Agreement [Member] | PREPA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Guarantor obligations, debt financing amount								2,000,000
Bridge Loan [Member] | AGM [Member] | Restructuring Support Agreement [Member] | PREPA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Guarantor obligations, debt financing amount								$ 13,000,000
Subsequent Event [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Payments Made To Public On Outstanding Principal Amounts		$ 41,000,000
Subsequent Event [Member] | AGM [Member] | PREPA [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Bonds issued in settlement		$ 26,000,000

[1] Excludes $1.4 billion of loss mitigation securities insured and held by the Company as of June 30, 2016, which are primarily BIG.

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

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

[4] Subsequent to June 30, 2016, and as a result of its July 1, 2016 Puerto Rico claim payments, the Company downgraded from BIG 1 to BIG 3 $1,803 million net par outstanding of financial guaranty insurance across two risks..