Subsidiary Information (Details 3) (USD $)	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Condensed financial statements
Net cash flows provided by (used in) operating activities	$ 162,138,000	$ 631,946,000
Fixed maturity securities:
Purchases	(923,704,000)	(1,349,745,000)
Sales	525,523,000	685,980,000
Maturities	514,725,000	325,750,000
Sales (purchases) of short-term investments, net	(108,014,000)	(49,901,000)
Net proceeds from financial guaranty variable entities' assets	282,790,000	423,977,000
Other	73,200,000	8,700,000
Acquisition of MIAC, net of cash acquired	(91,094,000)	0
Net cash flows provided by (used in) investing activities	273,400,000	44,800,000
Cash flows from financing activities
Issuance of common stock	172,500,000	0
Dividends paid	(32,878,000)	(16,577,000)
Share activity under option and incentive plans	(2,209,000)	(2,652,000)
Net paydowns of financial guaranty variable entities' liabilities	(388,576,000)	(593,294,000)
Payment of long-term debt	(195,668,000)	(10,294,000)
Net cash flows provided by (used in) financing activities	(471,144,000)	(622,817,000)
Repurchases of common stock	(24,313,000)	0
Effect of exchange rate changes	(3,649,000)	3,215,000
Increase (decrease) in cash	(39,197,000)	57,101,000
Cash at beginning of period	214,544,000	108,389,000
Cash at end of period	175,347,000	165,490,000
Assured Guaranty Ltd. (Parent)
Condensed financial statements
Net cash flows provided by (used in) operating activities	56,000,000	12,700,000
Fixed maturity securities:
Purchases	(91,600,000)
Sales (purchases) of short-term investments, net	(77,600,000)	6,500,000
Net cash flows provided by (used in) investing activities	(169,200,000)	6,500,000
Cash flows from financing activities
Issuance of common stock	172,500,000
Dividends paid	(32,900,000)	(16,600,000)
Share activity under option and incentive plans	(2,100,000)	(2,600,000)
Net cash flows provided by (used in) financing activities	113,200,000	(19,200,000)
Repurchases of common stock	(24,300,000)
Increase (decrease) in cash	0
Cash at beginning of period	0
Cash at end of period	0
AGUS (Issuer)
Condensed financial statements
Net cash flows provided by (used in) operating activities	24,900,000	6,600,000
Fixed maturity securities:
Purchases	(1,300,000)
Sales (purchases) of short-term investments, net	27,000,000	(17,300,000)
Acquisition of MIAC, net of cash acquired	(91,100,000)
Net cash flows provided by (used in) investing activities	(65,400,000)	(17,300,000)
Cash flows from financing activities
Payment of long-term debt	(172,500,000)
Financing Activities, Intercompany Debt	172,500,000
Increase (decrease) in cash	(40,500,000)	(10,700,000)
Cash at beginning of period	71,700,000	13,000,000
Cash at end of period	31,200,000	2,300,000
AGMH (Issuer)
Condensed financial statements
Net cash flows provided by (used in) operating activities	21,000,000	(13,000,000)
Fixed maturity securities:
Purchases	(10,400,000)	(300,000)
Sales	1,000,000
Maturities	1,500,000	400,000
Sales (purchases) of short-term investments, net	17,000,000	(12,100,000)
Investment in subsidiary		25,000,000
Investing Activities, Investment in Subsidiary	50,000,000
Net cash flows provided by (used in) investing activities	59,100,000	13,000,000
Cash flows from financing activities
Dividends paid	(80,000,000)
Net cash flows provided by (used in) financing activities	(80,000,000)
Increase (decrease) in cash	100,000
Cash at end of period	100,000
Other Subsidiaries
Condensed financial statements
Net cash flows provided by (used in) operating activities	295,500,000	659,600,000
Fixed maturity securities:
Purchases	(820,400,000)	(1,349,400,000)
Sales	524,500,000	686,000,000
Maturities	513,200,000	325,300,000
Sales (purchases) of short-term investments, net	(74,400,000)	(27,000,000)
Net proceeds from financial guaranty variable entities' assets	282,800,000	424,000,000
Investment in subsidiary	73,200,000
Other		8,700,000
Investing Activities, Intercompany Debt	(172,500,000)
Net cash flows provided by (used in) investing activities	326,400,000	67,600,000
Cash flows from financing activities
Proceeds from Return of Capital		(25,000,000)
Return of capital	(50,000,000)
Dividends paid	(155,300,000)	(34,000,000)
Net paydowns of financial guaranty variable entities' liabilities	(388,600,000)	(593,300,000)
Payment of long-term debt	(23,200,000)	(10,300,000)
Net cash flows provided by (used in) financing activities	(617,100,000)	(662,600,000)
Effect of exchange rate changes	(3,600,000)	3,200,000
Increase (decrease) in cash	1,200,000	67,800,000
Cash at beginning of period	142,800,000	95,400,000
Cash at end of period	144,000,000	163,200,000
Consolidating Adjustments
Condensed financial statements
Net cash flows provided by (used in) operating activities	(235,300,000)	(34,000,000)
Fixed maturity securities:
Investment in subsidiary		(25,000,000)
Investing Activities, Intercompany Debt	172,500,000
Investing Activities, Investment in Subsidiary	(50,000,000)
Net cash flows provided by (used in) investing activities	122,500,000	(25,000,000)
Cash flows from financing activities
Proceeds from Return of Capital		25,000,000
Return of capital	50,000,000
Dividends paid	235,300,000	34,000,000
Financing Activities, Intercompany Debt	(172,500,000)
Net cash flows provided by (used in) financing activities	$ 112,800,000	$ 59,000,000