Long-Term Debt and Credit Facilities - Interest Expense (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Interest expense	$ 92	$ 82	$ 92
AGUS [Member]
Debt Instrument [Line Items]
Interest expense	36	23	31
AGMH [Member]
Debt Instrument [Line Items]
Interest expense	54	54	54
AGM [Member]
Debt Instrument [Line Items]
Interest expense	2	5	7
Junior Subordinated Debt [Member] | AGMH [Member]
Debt Instrument [Line Items]
Interest expense	25	25	25
Corporate securities [Member] | AGMH [Member] | QUIBS 6.875 Percent [Member]
Debt Instrument [Line Items]
Interest expense	7	7	7
Senior Notes [Member] | AGUS [Member] | Senior Notes 7.0 Percent [Member]
Debt Instrument [Line Items]
Interest expense	13	13	13
Senior Notes [Member] | AGUS [Member] | Senior Notes 5.0 Percent [Member]
Debt Instrument [Line Items]
Interest expense	13	0	0
Senior Notes [Member] | AGUS [Member] | Senior Notes 8.50 Percent [Member]
Debt Instrument [Line Items]
Interest expense	0	0	8
Enhanced Junior Subordinated Debentures [Member] | AGUS [Member]
Debt Instrument [Line Items]
Interest expense	10	10	10
Notes Payable, Other Payables [Member] | AGMH [Member] | 6.25% Notes [Member]
Debt Instrument [Line Items]
Interest expense	16	16	16
Notes Payable, Other Payables [Member] | AGMH [Member] | Notes Payable 5.60 Percent [Member]
Debt Instrument [Line Items]
Interest expense	6	6	6
Notes Payable, Other Payables [Member] | AGM [Member]
Debt Instrument [Line Items]
Interest expense	$ 2	$ 5	$ 7