Long-Term Debt and Credit Facilities - Narrative (Details) (USD $)	1 Months Ended	0 Months Ended		12 Months Ended	0 Months Ended
	Jun. 30, 2003 Trust	Apr. 07, 2008	Nov. 22, 2006	Dec. 31, 2014 extension	Jul. 31, 2003	Nov. 26, 2002	May 18, 2004	Jun. 20, 2014	Jun. 24, 2009	Jun. 01, 2012		Dec. 31, 2013	Apr. 08, 2008	Apr. 08, 2005 Trust	Jun. 30, 2009	Oct. 25, 2013	Dec. 19, 2001	Dec. 20, 2006	Jun. 30, 2014	Jul. 01, 2009
Debt Instrument [Line Items]
Aggregate principal amount				$ 1,596,000,000								$ 1,114,000,000
Price per share of stock issued (in dollars per share)										12.85	[1]
AGC Trust Preferred Securities [Member]
Debt Instrument [Line Items]
Basis points				2.50%									1.10%
AGM Trust Preferred Securities [Member]
Debt Instrument [Line Items]
Basis points				2.00%
AGUS [Member]
Debt Instrument [Line Items]
Aggregate principal amount				850,000,000								350,000,000
AGM [Member]
Debt Instrument [Line Items]
Aggregate principal amount				16,000,000								34,000,000
AGM [Member] | AGM CPS securities [Member]
Debt Instrument [Line Items]
Maximum stock purchase obligation of each custodial trust	50,000,000.0
Aggregate maximum stock purchase obligation of the custodial trusts	200,000,000
Number of custodial trusts	4
Rate basis for income distributions	one-month LIBOR
Auction interval (in days)	28 days
AGC [Member] | AGM CPS securities [Member]
Debt Instrument [Line Items]
Maximum stock purchase obligation of each custodial trust														200,000,000
Aggregate maximum stock purchase obligation of the custodial trusts														50,000,000.0
Number of custodial trusts														4
Rate basis for income distributions		one-month LIBOR
AGMH [Member]
Debt Instrument [Line Items]
Aggregate principal amount				730,000,000								730,000,000
Junior Subordinated Debt [Member] | AGMH [Member]
Debt Instrument [Line Items]
Aggregate principal amount				300,000,000								300,000,000
Interest rate of debt (as a percent)				6.40%
Interest rate, added to base rate (as a percent)				2.215%
Debt issued			300,000,000
Number of times repayment date may be extended				4
Junior Subordinated Debt [Member] | Maximum [Member] | AGMH [Member]
Debt Instrument [Line Items]
Period for increments of repayment date extension				5 years
Line of Credit [Member] | Strip Coverage Facility [Member] | AGM [Member]
Debt Instrument [Line Items]
Cumulative strip par exposure terminated				1,400,000,000
Commitment amount				1,000,000,000
Covenant terms, additional net worth requirement under reduced borrowing capacity				0
Covenant terms, maximum debt-to-capital ratio															30.00%
Covenant terms, minimum net worth percentage															75.00%
Covenant terms, minimum percentage of aggregate consolidated net income (or loss)				25.00%
Line of Credit [Member] | Revolving Credit Facility [Member] | Wilbur L. Ross [Member]
Debt Instrument [Line Items]
Interest rate, as a percentage of Federal short-term or mid-term interest rate																100.00%
Notes Payable, Other Payables [Member] | AGM [Member]
Debt Instrument [Line Items]
Aggregate principal amount				16,000,000								34,000,000
Notes Payable 5.60 Percent [Member] | Notes Payable, Other Payables [Member] | AGMH [Member]
Debt Instrument [Line Items]
Aggregate principal amount				100,000,000								100,000,000
Interest rate of debt (as a percent)				5.60%								5.60%
Debt issued					100,000,000.0
6.25% Notes [Member] | Notes Payable, Other Payables [Member] | AGMH [Member]
Debt Instrument [Line Items]
Aggregate principal amount				230,000,000								230,000,000
Interest rate of debt (as a percent)				6.25%								6.25%
Debt issued						230,000,000.0
QUIBS 6.875 Percent [Member] | Corporate securities [Member] | AGMH [Member]
Debt Instrument [Line Items]
Aggregate principal amount				100,000,000								100,000,000					100,000,000.0
Interest rate of debt (as a percent)				6.875%								6.875%
Enhanced Junior Subordinated Debentures [Member] | Junior Subordinated Debt [Member] | AGUS [Member]
Debt Instrument [Line Items]
Aggregate principal amount																		150,000,000
Interest rate, added to base rate (as a percent)				2.38%
Enhanced Junior Subordinated Debentures [Member] | Junior Subordinated Debt [Member] | AGMH [Member]
Debt Instrument [Line Items]
Number of times interest payment may be deferred				1
Number of consecutive periods for which interest payments may be deferred				1
Period for which interest payment may be deferred (in years)				10 years
Period prior to final repayment date before which debt cannot be repaid, redeemed, repurchased or defeased (in years)				20 years
Senior Notes 8.50 Percent [Member] | Senior Notes [Member] | AGUS [Member]
Debt Instrument [Line Items]
Aggregate principal amount										173,000,000
Interest rate of debt (as a percent)				8.50%								8.50%
Principal amount of debt for percentage of undivided beneficial ownership interest per equity unit				1,000
Repurchase of debt, percent of principal amount				100.00%
Senior Notes 7.0 Percent [Member] | Senior Notes [Member] | AGUS [Member]
Debt Instrument [Line Items]
Aggregate principal amount				200,000,000			200,000,000.0					200,000,000
Net proceeds from issuance of debt							197,000,000
Interest rate of debt (as a percent)				7.00%			7.00%					7.00%
Effective interest rate of debt (as a percent)							6.40%
Senior Notes 5.0 Percent [Member] | Senior Notes [Member] | AGUS [Member]
Debt Instrument [Line Items]
Aggregate principal amount				500,000,000				500,000,000				0
Net proceeds from issuance of debt								495,000,000
Interest rate of debt (as a percent)				5.00%								0.00%
Intercompany Credit Facility [Member] | Line of Credit [Member] | Revolving Credit Facility [Member] | Wilbur L. Ross [Member] | AGL [Member]
Debt Instrument [Line Items]
Related party, maximum borrowing capacity																225,000,000
Registered Public Offering [Member] | Senior Notes 8.50 Percent [Member] | Senior Notes [Member] | AGUS [Member]
Debt Instrument [Line Items]
Shares issued									3,450,000
Proceeds from sales issued									167,000,000
Percentage of undivided beneficial ownership interest in debt principal per equity unit				5.00%
Price for which shares are issuable under forward purchase contract for each equity unit				50
Satisfaction of Forward Purchase Contract Obligation [Member] | AGL [Member]
Debt Instrument [Line Items]
AGL common shares issued for each $50 of proceeds received from remarketing Senior Notes										3.8924
Settlement rate in common shares after anti-dilution adjustments										3.8685
Common shares issued										13,428,770
Common Stock [Member] | Satisfaction of Forward Purchase Contract Obligation [Member] | AGL [Member]
Debt Instrument [Line Items]
Price per share of stock issued (in dollars per share)										12.85
Structured Finance [Member] | Financial Guarantee [Member] | AGM [Member]
Debt Instrument [Line Items]
Possible liquidity claims, gross exposure				1,200,000,000
Dexia Credit Local (NY) [Member] | Line of Credit [Member] | Strip Coverage Facility [Member] | AGM [Member]
Debt Instrument [Line Items]
Commitment amount																			$ 495,000,000	$ 1,000,000,000

[1] Relates to the settlement of forward purchase contracts. See Note 17, Long-Term Debt and Credit Facilities.