Long-Term Debt and Credit Facilities (Details 2) (USD $)	1 Months Ended											6 Months Ended		6 Months Ended
	Nov. 30, 2006 2006 Credit Facility Y D	Jun. 30, 2011 2006 Credit Facility Defaulters	Dec. 31, 2010 2006 Credit Facility	Jun. 30, 2009 2006 Credit Facility	Nov. 06, 2006 2006 Credit Facility	Jun. 30, 2011 2006 Credit Facility AGL, AG Re and/or AGRO	Jun. 30, 2011 2006 Credit Facility AGUK	Nov. 06, 2006 2006 Credit Facility AGC and Other Subsidiaries	Jun. 30, 2006 2006 Credit Facility AGC and Other Subsidiaries	Jun. 30, 2011 AGM 2009 Strip Coverage Facility Transactions	Jul. 01, 2009 AGM 2009 Strip Coverage Facility	Jun. 30, 2011 AG Re Credit Facility	Jul. 31, 2007 AG Re Credit Facility	Jun. 30, 2011 AGM Credit Facility	Apr. 30, 2005 AGM Credit Facility
Credit facilities
Maximum credit facility					$ 300,000,000	$ 100,000,000	$ 20,000,000			$ 988,400,000	$ 1,000,000,000		$ 200,000,000		$ 297,500,000
Term of revolving credit facility (in years)	5
Maximum amount of outstanding letters of credit and unpaid drawings in respect to all letters of credit		100,000,000
Potential increase to credit facility		100,000,000
Maximum expanded credit facility		400,000,000
Minimum increase to credit facility		25,000,000
Threshold consolidated assets for guarantee								1,200,000,000
Number of days to provide guarantee (in days)	15
Minimum net worth which is required to be maintained (as a percent)				75.00%							75.00%
Maximum debt-to-capital ratio which is required to be maintained (as a percent)		30.00%								30.00%
Minimum qualified statutory capital which is required to be maintained (as a percent)									75.00%
Minimum number of defaulters to trigger right to terminate		1
Outstanding letters of credit		2,900,000	2,900,000
Number of leveraged lease transactions due to 2008 downgrade										45
Liquidity claims on gross exposure										1,100,000,000
Number of leveraged lease transactions due to 2011 downgrade										26
Liquidity claims on additional gross exposure										1,000,000,000
Cumulative strip par exposure terminated										600,000,000
Reduced maximum credit facility for 2014 if consolidated net worth not maintained										750,000,000
Reduced commitment amount to trigger termination										0
Minimum percentage of aggregate consolidate net income (or loss) for July 1, 2009 through June 30, 2014 to be added to net worth requirement (as a percent)										25.00%
Amount to be added to net worth requirement if borrowing capacity is reduced										750,000,000
Threshold cumulative municipal losses to utilize credit facility												$ 260,000,000		$ 297,500,000
Threshold cumulative municipal losses as a percent of debt service to utilize credit facility (as a percent)												4.50%		5.00%