Long-Term Debt and Credit Facilities (Details 2) (USD $)					3 Months Ended
	Jun. 30, 2013	Jun. 30, 2013 2009 Strip Coverage Facility AGM	Jul. 01, 2009 2009 Strip Coverage Facility AGM	Jun. 30, 2009 2009 Strip Coverage Facility AGM	Jun. 30, 2013 AG Re Credit Facility	Apr. 08, 2005 Letter of credit agreement with Bank of New York Mellon AGC
Credit facilities
Liquidity claims on gross exposure		$ 1,700,000,000
Cumulative strip par exposure terminated		1,000,000,000
Maximum credit facility			1,000,000,000		200,000,000.0	2,900,000
Reduced commitment amount to trigger termination		981,000,000
Reduced maximum credit facility for 2014 if consolidated net worth not maintained		750,000,000
Amount to be added to net worth requirement if borrowing capacity is reduced		0
Maximum debt-to-capital ratio which is required to be maintained (as a percent)				30.00%
Minimum net worth which is required to be maintained (as a percent)				75.00%
Minimum percentage of aggregate consolidate net income (or loss) for July 1, 2009 through June 30, 2014 to be added to net worth requirement		25.00%
Threshold cumulative municipal losses to utilize credit facility					260,000,000
Threshold cumulative municipal losses as a percent of debt service to utilize credit facility					4.50%
Amount outstanding under letter of credit	$ 2,900,000