Consolidated Statement of Shareholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Total Shareholders' Equity Attributable to Assured Guaranty Ltd.	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income	Deferred Equity Compensation	Noncontrolling Interest of Financial Guaranty Consolidated Variable Interest Entities
Balance at Dec. 31, 2008 (Before Transition Adjustment)	$ 1,926,222	$ 1,926,222			$ 638,055
Balance (Transition Adjustment)	19,443	19,443			19,443
Balance at Dec. 31, 2008	1,945,665	1,945,665	910	1,284,370	657,498	2,887
Balance (in shares) at Dec. 31, 2008			90,955,703
Increase (Decrease) in Shareholders' Equity
Cumulative effect of change in accounting for other-than-temporary impairments effective April 1, 2009					57,652	(57,652)
Issuance of stock for acquisition of Assured Guaranty Municipal Holdings Inc.	275,875	275,875	222	275,653
Issuance of stock for acquisition of Assured Guaranty Municipal Holdings Inc. (in shares)			22,153,951
Consolidation of financial guaranty variable interest entities	778							778
Net income	84,822	85,978			85,978			(1,156)
Dividends on common stock ($0.18 per share)	(22,332)	(22,332)			(22,332)
Dividends on restricted stock units				135	(135)
Common stock issuance, net of offering costs	1,021,850	1,021,850	718	1,021,132
Common stock issuance, net of offering costs (in shares)			71,787,600
Common stock repurchases	(3,676)	(3,676)	(10)	(3,666)
Common stock repurchases (in shares)	(1,010,050)		(1,010,050)
Share-based compensation and other	9,361	9,361	2	7,359			2,000
Share-based compensation and other (in shares)			275,692
Change in cumulative translation adjustment	(3,000)	(3,029)				(3,029)		29
Change in cash flow hedge	(418)	(418)				(418)
Change in unrealized gains (losses) on:
Investments with no other-than-temporary impairment	177,307	177,307				177,307
Investments with other-than-temporary impairment	(11,378)	(11,378)				(11,378)
Less: reclassification adjustment for gains (losses) included in net income (loss)	(34,097)	(34,097)				(34,097)
Balance at Dec. 31, 2009 (Before Transition Adjustment)	3,508,951	3,509,300			778,661			(349)
Balance (Transition Adjustment)	(206,191)	(206,540)			(206,540)			349
Balance at Dec. 31, 2009	3,302,760	3,302,760	1,842	2,584,983	572,121	141,814	2,000
Balance (in shares) at Dec. 31, 2009			184,162,896
Increase (Decrease) in Shareholders' Equity
Net income	493,707	493,707			493,707
Dividends on common stock ($0.18 per share)	(33,190)	(33,190)			(33,190)
Dividends on restricted stock units				193	(193)
Common stock repurchases	(10,457)	(10,457)	(7)	(10,450)
Common stock repurchases (in shares)	(707,350)		(707,350)
Share-based compensation and other	10,699	10,699	2	10,697
Share-based compensation and other (in shares)			289,109
Change in cumulative translation adjustment	(384)	(384)				(384)
Change in cash flow hedge	(418)	(418)				(418)
Change in unrealized gains (losses) on:
Investments with no other-than-temporary impairment	(33,496)	(33,496)				(33,496)
Investments with other-than-temporary impairment	5,776	5,776				5,776
Less: reclassification adjustment for gains (losses) included in net income (loss)	1,543	1,543				1,543
Balance at Dec. 31, 2010	3,733,454	3,733,454	1,837	2,585,423	1,032,445	111,749	2,000
Balance (in shares) at Dec. 31, 2010			183,744,655
Increase (Decrease) in Shareholders' Equity
Net income	775,620	775,620			775,620
Dividends on common stock ($0.18 per share)	(33,035)	(33,035)			(33,035)
Dividends on restricted stock units				237	(237)
Common stock repurchases	(23,311)	(23,311)	(20)	(23,291)
Common stock repurchases (in shares)	(2,000,000)		(2,000,000)
Share-based compensation and other	9,958	9,958	5	7,553			2,400
Share-based compensation and other (in shares)			491,143
Change in cumulative translation adjustment	(779)	(779)				(779)
Change in cash flow hedge	(418)	(418)				(418)
Change in unrealized gains (losses) on:
Investments with no other-than-temporary impairment	233,970	233,970				233,970
Investments with other-than-temporary impairment	8,687	8,687				8,687
Less: reclassification adjustment for gains (losses) included in net income (loss)	(14,290)	(14,290)				(14,290)
Balance at Dec. 31, 2011	$ 4,718,436	$ 4,718,436	$ 1,822	$ 2,569,922	$ 1,774,793	$ 367,499	$ 4,400
Balance (in shares) at Dec. 31, 2011			182,235,798