Long-Term Debt and Credit Facilities - Interest Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Interest expense	$ 101	$ 92	$ 82
AGUS [Member]
Debt Instrument [Line Items]
Interest expense	49	36	23
AGMH [Member]
Debt Instrument [Line Items]
Interest expense	54	54	54
AGM [Member]
Debt Instrument [Line Items]
Interest expense	(2)	2	5
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	26	13	0
Series A 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)	$ 2	$ 5