Subsidiary Information (Details) (USD $)	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010
Assets
Total investment portfolio and cash	$ 11,494,200,000	$ 11,313,300,000
Premiums receivable, net of ceding commissions payable	1,018,672,000	1,002,852,000	1,118,000,000	1,167,600,000
Ceded unearned premium reserve	631,398,000	708,872,000
Deferred acquisition costs	129,015,000	132,418,000
Reinsurance recoverable on unpaid losses	152,898,000	69,300,000
Credit derivative assets	463,556,000	468,933,000
Deferred tax asset, net	1,031,805,000	803,529,000
Financial guaranty variable interest entities' assets, at fair value	2,827,652,000	2,819,077,000
Other	755,500,000	706,400,000
Total assets	18,504,813,000	18,024,660,000
Liabilities and shareholders' equity
Unearned premium reserves	5,839,223,000	5,962,799,000
Loss and LAE reserve	954,475,000	679,011,000
Long-term debt	1,034,667,000	1,038,302,000
Credit derivative liabilities	2,416,268,000	1,772,803,000
Financial guaranty variable interest entities' liabilities, at fair value	3,450,800,000	3,458,400,000
Other	626,800,000	461,800,000
Total liabilities	14,322,295,000	13,373,095,000
Total shareholders' equity	4,182,518,000	4,651,565,000
Total liabilities and shareholders' equity	18,504,813,000	18,024,660,000
Assured Guaranty Ltd. (Parent)
Assets
Total investment portfolio and cash	43,200,000	32,900,000
Investment in subsidiaries	4,131,100,000	4,606,700,000
Other	16,300,000	23,100,000
Total assets	4,190,600,000	4,662,700,000
Liabilities and shareholders' equity
Other	8,100,000	11,100,000
Total liabilities	8,100,000	11,100,000
Total shareholders' equity	4,182,500,000	4,651,600,000
Total liabilities and shareholders' equity	4,190,600,000	4,662,700,000
AGUS (Issuer)
Assets
Total investment portfolio and cash	31,900,000	99,500,000
Investment in subsidiaries	3,357,200,000	3,730,000,000
Deferred tax asset, net	22,300,000	22,500,000
Other	40,800,000	(71,300,000)
Total assets	3,452,200,000	3,780,700,000
Liabilities and shareholders' equity
Long-term debt	519,800,000	519,500,000
Credit derivative liabilities	200,000	200,000
Other	8,900,000	2,900,000
Total liabilities	528,900,000	522,600,000
Total shareholders' equity	2,923,300,000	3,258,100,000
Total liabilities and shareholders' equity	3,452,200,000	3,780,700,000
AGMH (Issuer)
Assets
Total investment portfolio and cash	68,100,000	61,400,000
Investment in subsidiaries	2,785,600,000	2,801,300,000
Deferred tax asset, net	(76,100,000)	(76,900,000)
Other	21,600,000	26,900,000
Total assets	2,799,200,000	2,812,700,000
Liabilities and shareholders' equity
Long-term debt	417,000,000	415,100,000
Other	20,900,000	15,700,000
Total liabilities	437,900,000	430,800,000
Total shareholders' equity	2,361,300,000	2,381,900,000
Total liabilities and shareholders' equity	2,799,200,000	2,812,700,000
Other Subsidiaries
Assets
Total investment portfolio and cash	11,351,000,000	11,119,500,000
Investment in subsidiaries	2,923,300,000	3,258,100,000
Premiums receivable, net of ceding commissions payable	1,159,700,000	1,149,600,000
Ceded unearned premium reserve	1,654,400,000	1,739,100,000
Deferred acquisition costs	216,400,000	223,300,000
Reinsurance recoverable on unpaid losses	333,700,000	211,800,000
Credit derivative assets	490,300,000	503,400,000
Deferred tax asset, net	1,098,400,000	867,200,000
Intercompany receivable	300,000,000	300,000,000
Financial guaranty variable interest entities' assets, at fair value	2,827,700,000	2,819,100,000
Other	811,200,000	836,500,000
Total assets	23,166,100,000	23,027,600,000
Liabilities and shareholders' equity
Unearned premium reserves	6,822,800,000	6,949,400,000
Loss and LAE reserve	1,148,500,000	834,200,000
Long-term debt	97,900,000	103,700,000
Intercompany payable	300,000,000	300,000,000
Credit derivative liabilities	2,442,800,000	1,807,100,000
Financial guaranty variable interest entities' liabilities, at fair value	3,450,800,000	3,458,400,000
Other	847,000,000	674,700,000
Total liabilities	15,109,800,000	14,127,500,000
Total shareholders' equity	8,056,300,000	8,900,100,000
Total liabilities and shareholders' equity	23,166,100,000	23,027,600,000
Consolidating Adjustments
Assets
Investment in subsidiaries	(13,197,200,000)	(14,396,100,000)
Premiums receivable, net of ceding commissions payable	(141,000,000)	(146,700,000)
Ceded unearned premium reserve	(1,023,000,000)	(1,030,200,000)
Deferred acquisition costs	(87,400,000)	(90,900,000)
Reinsurance recoverable on unpaid losses	(180,800,000)	(142,500,000)
Credit derivative assets	(26,700,000)	(34,500,000)
Deferred tax asset, net	(12,800,000)	(9,300,000)
Intercompany receivable	(300,000,000)	(300,000,000)
Other	(134,400,000)	(108,800,000)
Total assets	(15,103,300,000)	(16,259,000,000)
Liabilities and shareholders' equity
Unearned premium reserves	(983,600,000)	(986,600,000)
Loss and LAE reserve	(194,000,000)	(155,200,000)
Intercompany payable	(300,000,000)	(300,000,000)
Credit derivative liabilities	(26,700,000)	(34,500,000)
Other	(258,100,000)	(242,600,000)
Total liabilities	(1,762,400,000)	(1,718,900,000)
Total shareholders' equity	(13,340,900,000)	(14,540,100,000)
Total liabilities and shareholders' equity	$ (15,103,300,000)	$ (16,259,000,000)