Long-Term Debt and Credit Facilities - Interest Expense (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Interest expense	$ 19	$ 21	$ 21	$ 21	$ 21	$ 21	$ 25	$ 25	$ 82	$ 92	$ 99
AGUS
Debt Instrument [Line Items]
Interest expense									23	31	39
AGUS | 7.0% Senior Notes
Debt Instrument [Line Items]
Interest expense									13	13	13
AGUS | 8.50% Senior Notes
Debt Instrument [Line Items]
Interest expense									0	8	16
AGUS | Series A Enhanced Junior Subordinated Debentures
Debt Instrument [Line Items]
Interest expense									10	10	10
AGMH
Debt Instrument [Line Items]
Interest expense									54	54	54
AGMH | 6 7/8% QUIBS
Debt Instrument [Line Items]
Interest expense									7	7	7
AGMH | 6.25% Notes
Debt Instrument [Line Items]
Interest expense									16	16	16
AGMH | 5.60% Notes
Debt Instrument [Line Items]
Interest expense									6	6	6
AGMH | Junior Subordinated Debentures
Debt Instrument [Line Items]
Interest expense									25	25	25
AGM
Debt Instrument [Line Items]
Interest expense									5	7	6
AGM | Notes Payable
Debt Instrument [Line Items]
Interest expense									$ 5	$ 7	$ 6