Subsidiary Information (Details 3) (USD $)	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2007
Condensed financial statements
Net cash flows provided by (used in) operating activities	$ 631,946,000	$ (217,674,000)
Fixed maturity securities:
Purchases	(1,349,745,000)	(1,166,379,000)
Sales	685,980,000	780,818,000
Maturities	325,750,000	488,552,000
Sales (purchases) of short-term investments, net	(49,901,000)	248,780,000
Net proceeds from financial guaranty variable entities' assets	423,977,000	217,329,000
Other	8,696,000	8,317,000
Net cash flows provided by (used in) investing activities	44,757,000	577,417,000
Cash flows from financing activities
Dividends paid	(16,577,000)	(16,613,000)
Repurchases of common stock		(10,457,000)
Share activity under option and incentive plans	(2,652,000)	(2,233,000)
Net paydowns of financial guaranty variable entities' liabilities	(593,294,000)	(259,367,000)
Payment of long-term debt	(10,294,000)	(10,850,000)
Net cash flows provided by (used in) financing activities	(622,817,000)	(299,520,000)
Effect of foreign exchange rate changes	3,215,000	(3,090,000)
Increase (decrease) in cash	57,101,000	57,133,000
Cash at beginning of period	108,389,000	44,133,000
Cash at end of period	165,490,000	101,266,000
Total Shareholders' Equity Attributable to Assured Guaranty Ltd.
Condensed financial statements
Net cash flows provided by (used in) operating activities	12,700,000	(2,100,000)
Fixed maturity securities:
Sales (purchases) of short-term investments, net	6,500,000	31,500,000
Net cash flows provided by (used in) investing activities	6,500,000	31,500,000
Cash flows from financing activities
Dividends paid	(16,600,000)	(16,600,000)
Repurchases of common stock		(10,500,000)
Share activity under option and incentive plans	(2,600,000)	(2,300,000)
Net cash flows provided by (used in) financing activities	(19,200,000)	(29,400,000)
AGUS (Issuer)
Condensed financial statements
Net cash flows provided by (used in) operating activities	6,600,000	10,700,000
Fixed maturity securities:
Sales (purchases) of short-term investments, net	(17,300,000)	(10,800,000)
Net cash flows provided by (used in) investing activities	(17,300,000)	(10,800,000)
Cash flows from financing activities
Increase (decrease) in cash	(10,700,000)	(100,000)
Cash at beginning of period	13,000,000	100,000
Cash at end of period	2,300,000
AGMH (Issuer)
Condensed financial statements
Net cash flows provided by (used in) operating activities	(13,000,000)	(25,100,000)
Fixed maturity securities:
Purchases	(300,000)
Maturities	400,000	4,100,000
Sales (purchases) of short-term investments, net	(12,100,000)	(2,400,000)
Investment in subsidiary	25,000,000	25,000,000
Net cash flows provided by (used in) investing activities	13,000,000	26,700,000
Cash flows from financing activities
Increase (decrease) in cash		1,600,000
Cash at end of period		1,600,000
Other Subsidiaries
Condensed financial statements
Net cash flows provided by (used in) operating activities	659,600,000	(171,100,000)
Fixed maturity securities:
Purchases	(1,349,400,000)	(1,166,300,000)
Sales	686,000,000	780,800,000
Maturities	325,300,000	484,500,000
Sales (purchases) of short-term investments, net	(27,000,000)	230,400,000
Net proceeds from financial guaranty variable entities' assets	424,000,000	217,300,000
Other	8,700,000	8,300,000
Net cash flows provided by (used in) investing activities	67,600,000	555,000,000
Cash flows from financing activities
Return of capital	(25,000,000)	(25,000,000)
Dividends paid	(34,000,000)	(30,000,000)
Net paydowns of financial guaranty variable entities' liabilities	(593,300,000)	(259,400,000)
Payment of long-term debt	(10,300,000)	(10,800,000)
Net cash flows provided by (used in) financing activities	(662,600,000)	(325,200,000)
Effect of foreign exchange rate changes	3,200,000	(3,100,000)
Increase (decrease) in cash	67,800,000	55,600,000
Cash at beginning of period	95,400,000	44,000,000	8,000,000
Cash at end of period	163,200,000	99,600,000	8,000,000
Consolidating Adjustments
Condensed financial statements
Net cash flows provided by (used in) operating activities	(34,000,000)	(30,000,000)
Fixed maturity securities:
Investment in subsidiary	(25,000,000)	(25,000,000)
Net cash flows provided by (used in) investing activities	(25,000,000)	(25,000,000)
Cash flows from financing activities
Return of capital	25,000,000	25,000,000
Dividends paid	34,000,000	30,000,000
Net cash flows provided by (used in) financing activities	$ 59,000,000	$ 55,000,000