Long-Term Debt and Credit Facilities - Principal and Carrying Amounts of Debt (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Debt
Principal	$ 1,109	$ 1,114
Carrying Value	812	816
AGUS Consolidated
Debt
Principal	350	350
Carrying Value	348	348
AGUS Consolidated | 7.0% Senior Notes
Debt
Interest rate of debt (as a percent)	7.00%	7.00%
Principal	200	200
Carrying Value	198	198
AGUS Consolidated | Series A Enhanced Junior Subordinated Debentures
Debt
Principal	150	150
Carrying Value	150	150
AGMH Consolidated
Debt
Principal	730	730
Carrying Value	431	430
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	138
AGMH Consolidated | 5.60% Notes
Debt
Interest rate of debt (as a percent)	5.60%	5.60%
Principal	100	100
Carrying Value	55	55
AGMH Consolidated | Junior Subordinated Debentures
Debt
Principal	300	300
Carrying Value	170	169
AGM | AGM Notes Payable
Debt
Principal	29	34
Carrying Value	$ 33	$ 38