Long-Term Debt and Credit Facilities (Details) (USD $)	Jun. 30, 2012		Dec. 31, 2011
Debt
Principal	$ 1,153,900,000		$ 1,349,600,000
Carrying Value	846,354,000		1,038,302,000
AGUS (Consolidated)
Debt
Principal	350,000,000		522,500,000
Carrying Value	347,500,000		519,500,000
AGUS (Consolidated) | 7.0% Senior Notes
Debt
Principal	200,000,000		200,000,000
Carrying Value	197,600,000		197,600,000
Interest rate of debt (as a percent)	7.00%		7.00%
AGUS (Consolidated) | 8.50% Senior Notes
Debt
Principal	0	[1]	172,500,000	[1]
Carrying Value	0	[1]	172,000,000	[1]
Interest rate of debt (as a percent)	8.50%		8.50%
AGUS (Consolidated) | Series A Enhanced Junior Subordinated Debentures
Debt
Principal	150,000,000		150,000,000
Carrying Value	149,900,000		149,900,000
AGMH (Consolidated)
Debt
Principal	730,000,000		730,000,000
Carrying Value	418,900,000		415,100,000
AGMH (Consolidated) | 6 7/8% QUIBS
Debt
Principal	100,000,000		100,000,000
Carrying Value	67,600,000		67,400,000
Interest rate of debt (as a percent)	6.875%		6.875%
AGMH (Consolidated) | 6.25% Notes
Debt
Principal	230,000,000		230,000,000
Carrying Value	136,500,000		136,000,000
Interest rate of debt (as a percent)	6.25%		6.25%
AGMH (Consolidated) | 5.60% Notes
Debt
Principal	100,000,000		100,000,000
Carrying Value	53,800,000		53,500,000
Interest rate of debt (as a percent)	5.60%		5.60%
AGMH (Consolidated) | Junior Subordinated Debentures
Debt
Principal	300,000,000		300,000,000
Carrying Value	161,000,000		158,200,000
AGM
Debt
Principal	73,900,000		97,100,000
Carrying Value	80,000,000		103,700,000
AGM | Notes Payable
Debt
Principal	73,900,000		97,100,000
Carrying Value	$ 80,000,000		$ 103,700,000

[1] On June 1, 2012, AGUS retired all of the Senior Notes that it purchased in the remarketing. See Note 2, Business Changes, Risks, Uncertainties and Accounting Developments.