Expected Losses to be Paid - Components of R&W Development (Details)	3 Months Ended					3 Months Ended						3 Months Ended					3 Months Ended					3 Months Ended					3 Months Ended					3 Months Ended					3 Months Ended			3 Months Ended				12 Months Ended																														3 Months Ended
	Mar. 31, 2014 USD ($) risk		Mar. 31, 2013 USD ($)	Dec. 31, 2013 USD ($) risk		Mar. 31, 2014 Life Insurance [Member] USD ($)	Mar. 31, 2014 Prime first lien USD ($) risk		Mar. 31, 2013 Prime first lien USD ($)	Dec. 31, 2013 Prime first lien USD ($) risk		Mar. 31, 2014 Alt-A first lien USD ($) risk		Mar. 31, 2013 Alt-A first lien USD ($)	Dec. 31, 2013 Alt-A first lien USD ($) risk		Mar. 31, 2014 Option ARM USD ($) risk		Mar. 31, 2013 Option ARM USD ($)	Dec. 31, 2013 Option ARM USD ($) risk		Mar. 31, 2014 First mortgage, subprime USD ($) risk		Mar. 31, 2013 First mortgage, subprime USD ($)	Dec. 31, 2013 First mortgage, subprime USD ($) risk		Mar. 31, 2014 Closed end second lien and HELOCs USD ($) risk		Mar. 31, 2013 Closed end second lien and HELOCs USD ($)	Dec. 31, 2013 Closed end second lien and HELOCs USD ($) risk		Mar. 31, 2014 HELOCs USD ($) risk		Mar. 31, 2013 HELOCs USD ($)	Dec. 31, 2013 HELOCs USD ($) risk		Mar. 31, 2014 Student Loan [Member] USD ($)	Mar. 31, 2014 Asset-backed Student Loan [Member] USD ($)	Mar. 31, 2014 Public Finance Student Loan [Member] USD ($)	Mar. 31, 2014 Trust Preferred Securities Collateralized Debt Obligations USD ($)	Mar. 31, 2014 Public Finance City of Detroit [Member] USD ($)	Mar. 31, 2014 Public Finance Stockton General Fund [Member] USD ($)	Mar. 31, 2014 Public Finance Luoisville Arena Authority [Member] USD ($)	Dec. 31, 2013 Troubled Municipal Credits [Member] USD ($)	Mar. 31, 2014 Troubled Municipal Credits [Member] USD ($)	Mar. 31, 2014 Spanish sub-sovereign debt [Member] EUR (€)	Mar. 31, 2014 Portugal sub-sovereign debt [Member] EUR (€)	Mar. 31, 2014 Hungarian-infrastructure bonds [Member] USD ($)	Mar. 31, 2014 Spanish and Hungarian Debt [Member] USD ($)	Mar. 31, 2014 Manufactured Housing Loans [Member] USD ($)	Dec. 31, 2013 Manufactured Housing Loans [Member] USD ($)	Mar. 31, 2014 Below investment grade (BIG) USD ($)	Dec. 31, 2013 Below investment grade (BIG) USD ($)	Mar. 31, 2014 Below investment grade (BIG) Life Insurance [Member] USD ($)	Mar. 31, 2014 Below investment grade (BIG) Prime first lien USD ($)	Dec. 31, 2013 Below investment grade (BIG) Prime first lien USD ($)	Mar. 31, 2014 Below investment grade (BIG) Alt-A first lien USD ($)	Dec. 31, 2013 Below investment grade (BIG) Alt-A first lien USD ($)	Mar. 31, 2014 Below investment grade (BIG) Option ARM USD ($)	Dec. 31, 2013 Below investment grade (BIG) Option ARM USD ($)	Mar. 31, 2014 Below investment grade (BIG) First mortgage, subprime USD ($)	Dec. 31, 2013 Below investment grade (BIG) First mortgage, subprime USD ($)	Mar. 31, 2014 Below investment grade (BIG) HELOCs USD ($)	Dec. 31, 2013 Below investment grade (BIG) HELOCs USD ($)	Mar. 31, 2014 Below investment grade (BIG) Asset-backed Student Loan [Member] USD ($)	Mar. 31, 2014 Below investment grade (BIG) Public Finance Student Loan [Member] USD ($)	Mar. 31, 2014 Below investment grade (BIG) Trust Preferred Securities Collateralized Debt Obligations USD ($)	Mar. 31, 2014 Below investment grade (BIG) Manufactured Housing Loans [Member] USD ($)	Mar. 31, 2014 Below investment grade (BIG) Ballantyne Re Plc and Orkney Re I I Plc [Member] Life Insurance [Member] Transaction	Mar. 31, 2014 Sewer [Member] Public Finance City of Detroit [Member] USD ($)	Mar. 31, 2014 Water Sector [Member] Public Finance City of Detroit [Member] USD ($)	Mar. 31, 2014 Municipal Bonds State General Obligation [Member] Public Finance City of Detroit [Member] USD ($)	Mar. 31, 2014 City Certificates of Participation [Member] Public Finance City of Detroit [Member] USD ($)	Mar. 31, 2014 Refinancing Risk on Infrastructure Transactions [Member] USD ($) Transaction	Mar. 31, 2014 Refinancing Risk on Infrastructure Transactions [Member] Minimum	Mar. 31, 2014 Refinancing Risk on Infrastructure Transactions [Member] Maximum	Mar. 31, 2014 Puerto Rico USD ($)	Mar. 31, 2014 Puerto Rico Below investment grade (BIG) USD ($)	Mar. 31, 2014 Puerto Rico Below investment grade (BIG) USD ($)
Guarantor Obligations [Line Items]
Net par outstanding amount	$ 5,804,000,000																																				$ 2,800,000,000	$ 1,900,000,000	$ 900,000,000	$ 4,800,000,000										$ 248,000,000				$ 2,700,000,000											$ 204,000,000	$ 251,000,000	$ 1,600,000,000	$ 175,000,000		$ 1,000,000,000	$ 784,000,000	$ 146,000,000	$ 175,000,000	$ 3,000,000,000
Recovery Percentage																																									74.00%
Estimated Years for Recoveries on Infrastructure Transactions																																																																											10 years	35 years
Financial Guaranty Insurance Contracts Principal Amount, Percent in Credit Default Swap Form																																								71.00%
Number of Risks as of the end of the period with R&W Benefit Recorded (in policies)	45	[1]		42	[1]		1	[1]		1	[1]	20	[1]		19	[1]	10	[1]		9	[1]	5	[1]		5	[1]	4	[1]		4	[1]	5	[1]		4	[1]
Outstanding Principal and Interest on Representations and Warranties Policies	4,697,000,000			5,011,000,000			36,000,000			38,000,000		2,791,000,000			2,856,000,000		589,000,000			641,000,000		985,000,000			998,000,000		155,000,000			158,000,000		141,000,000			320,000,000
Change in recovery assumptions as the result of additional file review and recovery success	10,000,000		11,000,000
Estimated increase (decrease) in defaults that will result in additional (lower) breaches	0		1,000,000
Settlements and anticipated settlements	35,000,000		142,000,000
Accretion of discount on balance	3,000,000		3,000,000
Total	48,000,000		157,000,000				(1,000,000)		0			3,000,000		(8,000,000)			9,000,000		153,000,000			28,000,000		4,000,000			(3,000,000)		(9,000,000)			12,000,000		17,000,000
Loss and loss adjustment expense reserve	636,000,000			592,000,000																																																		598,000,000
Number of Transactions Insured																																																																					2
Projected Expected Loss to be Paid																																					68,000,000			32,000,000				264,000,000	281,000,000									85,000,000
Financial Guaranty Insurance Contracts Principal Amount Gross																																														435,000,000	92,000,000	623,000,000
Liability for Unpaid Claims and Claims Adjustment Expense Net Largest Single Loss																																					28,000,000													27,000,000	26,000,000
Increase (Decrease) in Projected Expected Loss to be Paid						12,000,000																															4,000,000			19,000,000				17,000,000
Insured Financial Obligations Outstanding Principal Amount Excluding Loss Mitigation Bonds	449,625,000,000			459,107,000,000			528,000,000			541,000,000		3,478,000,000			3,590,000,000		877,000,000			937,000,000		5,921,000,000			6,130,000,000							1,982,000,000			2,279,000,000																	21,943,000,000	22,538,000,000		395,000,000	403,000,000	2,713,000,000	2,728,000,000	565,000,000	598,000,000	1,856,000,000	1,945,000,000	1,734,000,000	1,897,000,000													5,300,000,000	5,073,000,000	5,100,000,000
Financial Guaranty Insurance Contracts Principal Amount Net																																									2,100,000,000	119,000,000	337,000,000			312,000,000	80,000,000	587,000,000
Expected LAE for mitigating claim liabilities	29,000,000			34,000,000																																													51,000,000
Claims Paid, Net																																										32,000,000
Number of Infrastructure Transactions																																																																										2
Financial Insurance Guaranty, Infrastructure Finance, Potential Liability																																																																										$ 1,800,000,000

[1] A risk represents the aggregate of the financial guaranty policies that share the same revenue source for purposes of making Debt Service payments. This table shows the full future Debt Service (not just the amount of Debt Service expected to be reimbursed) for risks with projected future R&W benefit, whether pursuant to an agreement or not.