Subsidiary Information (Details) (USD $)	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Assets
Total investment portfolio and cash	$ 11,313,300,000	$ 10,849,300,000
Premiums receivable, net of ceding commissions payable	1,002,852,000	1,167,587,000	1,418,200,000	15,700,000
Ceded unearned premium reserve	708,872,000	821,819,000
Deferred acquisition costs	231,875,000	239,805,000	242,000,000	288,600,000
Reinsurance recoverable on unpaid losses	69,300,000	22,255,000
Credit derivative assets	468,933,000	592,898,000
Deferred tax asset, net	770,943,000	1,259,125,000	1,274,200,000
Financial guaranty variable interest entities' assets, at fair value	2,819,077,000	3,657,481,000	1,925,300,000
Other assets	706,300,000	1,231,600,000
Total assets	18,091,531,000	19,841,919,000	18,034,500,000
Liabilities and shareholders' equity
Unearned premium reserves	5,962,799,000	6,972,894,000	8,268,000,000
Loss and LAE reserve	679,011,000	574,369,000	306,400,000
Long-term debt	1,038,302,000	1,052,936,000
Credit derivative liabilities	1,772,803,000	2,462,831,000
Financial guaranty variable interest entities' liabilities, at fair value	3,458,400,000	4,368,100,000
Other liabilities	461,800,000	677,300,000
Total liabilities	13,373,095,000	16,108,465,000	14,731,700,000
Total shareholders' equity	4,718,436,000	3,733,454,000	3,302,760,000	1,945,665,000
Total liabilities and shareholders' equity	18,091,531,000	19,841,919,000	18,034,500,000
Total Shareholders' Equity Attributable to Assured Guaranty Ltd.
Assets
Total investment portfolio and cash	32,900,000	22,500,000
Investment in subsidiaries	4,673,500,000	3,703,600,000
Other assets	23,100,000	19,200,000
Total assets	4,729,500,000	3,745,300,000
Liabilities and shareholders' equity
Other liabilities	11,100,000	11,800,000
Total liabilities	11,100,000	11,800,000
Total shareholders' equity	4,718,400,000	3,733,500,000
Total liabilities and shareholders' equity	4,729,500,000	3,745,300,000
AGUS (Issuer)
Assets
Total investment portfolio and cash	99,500,000	15,700,000
Investment in subsidiaries	3,790,500,000	2,965,400,000
Deferred tax asset, net	22,500,000	(800,000)
Other assets	(71,300,000)	3,800,000
Total assets	3,841,200,000	2,984,100,000
Liabilities and shareholders' equity
Long-term debt	519,500,000	518,400,000
Credit derivative liabilities	200,000	200,000
Other liabilities	2,900,000	(24,300,000)
Total liabilities	522,600,000	494,300,000
Total shareholders' equity	3,318,600,000	2,489,800,000
Total liabilities and shareholders' equity	3,841,200,000	2,984,100,000
AGMH
Assets
Total investment portfolio and cash	61,400,000	45,700,000
Investment in subsidiaries	2,814,100,000	2,316,900,000
Deferred tax asset, net	(76,900,000)	(95,800,000)
Other assets	26,900,000	15,200,000
Total assets	2,825,500,000	2,282,000,000
Liabilities and shareholders' equity
Long-term debt	415,100,000	407,500,000
Other liabilities	15,700,000	(6,900,000)
Total liabilities	430,800,000	400,600,000
Total shareholders' equity	2,394,700,000	1,881,400,000
Total liabilities and shareholders' equity	2,825,500,000	2,282,000,000
Other Subsidiaries
Assets
Total investment portfolio and cash	11,119,500,000	10,765,400,000
Investment in subsidiaries	3,318,600,000	2,489,800,000
Premiums receivable, net of ceding commissions payable	1,149,600,000	1,346,800,000
Ceded unearned premium reserve	1,739,100,000	1,883,400,000
Deferred acquisition costs	322,800,000	350,400,000
Reinsurance recoverable on unpaid losses	211,800,000	93,100,000
Credit derivative assets	503,400,000	672,700,000
Deferred tax asset, net	834,600,000	1,355,300,000
Intercompany receivable	300,000,000	300,000,000
Financial guaranty variable interest entities' assets, at fair value	2,819,100,000	3,657,500,000
Other assets	836,400,000	1,354,500,000
Total assets	23,154,900,000	24,268,900,000
Liabilities and shareholders' equity
Unearned premium reserves	6,949,400,000	7,976,500,000
Loss and LAE reserve	834,200,000	663,900,000
Long-term debt	103,700,000	127,000,000
Intercompany payable	300,000,000	300,000,000
Credit derivative liabilities	1,807,100,000	2,542,500,000
Financial guaranty variable interest entities' liabilities, at fair value	3,458,400,000	4,368,100,000
Other liabilities	674,700,000	1,023,700,000
Total liabilities	14,127,500,000	17,001,700,000
Total shareholders' equity	9,027,400,000	7,267,200,000
Total liabilities and shareholders' equity	23,154,900,000	24,268,900,000
Consolidating Adjustments
Assets
Investment in subsidiaries	(14,596,700,000)	(11,475,700,000)
Premiums receivable, net of ceding commissions payable	(146,700,000)	(179,200,000)
Ceded unearned premium reserve	(1,030,200,000)	(1,061,600,000)
Deferred acquisition costs	(90,900,000)	(110,600,000)
Reinsurance recoverable on unpaid losses	(142,500,000)	(70,800,000)
Credit derivative assets	(34,500,000)	(79,800,000)
Deferred tax asset, net	(9,300,000)	400,000
Intercompany receivable	(300,000,000)	(300,000,000)
Other assets	(108,800,000)	(161,100,000)
Total assets	(16,459,600,000)	(13,438,400,000)
Liabilities and shareholders' equity
Unearned premium reserves	(986,600,000)	(1,003,600,000)
Loss and LAE reserve	(155,200,000)	(89,500,000)
Intercompany payable	(300,000,000)	(300,000,000)
Credit derivative liabilities	(34,500,000)	(79,900,000)
Other liabilities	(242,600,000)	(327,000,000)
Total liabilities	(1,718,900,000)	(1,800,000,000)
Total shareholders' equity	(14,740,700,000)	(11,638,400,000)
Total liabilities and shareholders' equity	$ (16,459,600,000)	$ (13,438,400,000)