Long-Term Debt and Credit Facilities - Principal and Carrying Amounts of Debt (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	May 18, 2004
Debt Instrument [Line Items]
Principal	$ 1,114	$ 1,141
Carrying Value	816	836
AGUS
Debt Instrument [Line Items]
Principal	350	350
Carrying Value	348	347
AGUS | 7.0% Senior Notes
Debt Instrument [Line Items]
Principal	200	200
Carrying Value	198	197
Interest rate of debt (as a percent)	7.00%	7.00%	7.00%
AGUS | 8.50% Senior Notes
Debt Instrument [Line Items]
Principal	0	0
Carrying Value	0	0
Interest rate of debt (as a percent)	8.50%	8.50%
AGUS | Enhanced Junior Subordinated Debentures
Debt Instrument [Line Items]
Principal	150	150
Carrying Value	150	150
AGMH
Debt Instrument [Line Items]
Principal	730	730
Carrying Value	430	423
AGMH | 6 7/8% QUIBS
Debt Instrument [Line Items]
Principal	100	100
Carrying Value	68	68
Interest rate of debt (as a percent)	6.875%	6.875%
AGMH | 6.25% Notes
Debt Instrument [Line Items]
Principal	230	230
Carrying Value	138	137
Interest rate of debt (as a percent)	6.25%	6.25%
AGMH | 5.60% Notes
Debt Instrument [Line Items]
Principal	100	100
Carrying Value	55	54
Interest rate of debt (as a percent)	5.60%	5.60%
AGMH | Junior Subordinated Debentures
Debt Instrument [Line Items]
Principal	300	300
Carrying Value	169	164
Interest rate of debt (as a percent)	6.40%
AGM
Debt Instrument [Line Items]
Principal	34	61
Carrying Value	38	66
AGM | Notes Payable
Debt Instrument [Line Items]
Principal	34	61
Carrying Value	$ 38	$ 66