Long-Term Debt and Credit Facilities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Debt
Principal	$ 1,118	$ 1,141
Carrying Value	819	836
AGUS Consolidated
Debt
Principal	350	350
Carrying Value	348	347
AGUS Consolidated | 7.0% Senior Notes
Debt
Interest rate of debt (as a percent)	7.00%	7.00%
Principal	200	200
Carrying Value	198	197
AGUS Consolidated | Series A Enhanced Junior Subordinated Debentures
Debt
Principal	150	150
Carrying Value	150	150
AGMH Consolidated
Debt
Principal	730	730
Carrying Value	428	423
AGMH Consolidated | 6 7/8% QUIBS
Debt
Interest rate of debt (as a percent)	6.875%	6.875%
Principal	100	100
Carrying Value	68	68
AGMH Consolidated | 6.25% Notes
Debt
Interest rate of debt (as a percent)	6.25%	6.25%
Principal	230	230
Carrying Value	138	137
AGMH Consolidated | 5.60% Notes
Debt
Interest rate of debt (as a percent)	5.60%	5.60%
Principal	100	100
Carrying Value	54	54
AGMH Consolidated | Junior Subordinated Debentures
Debt
Principal	300	300
Carrying Value	168	164
AGM
Debt
Principal	38	61
Carrying Value	43	66
AGM | Notes Payable
Debt
Principal	38	61
Carrying Value	$ 43	$ 66