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Debt Instrument, Covenant Compliance, Annual Repayment, Percent of Principal, Years Six Through Nine

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Represents the period for which interest payments may be deferred by the entity.

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Represents the number of times the repayment date may be extended.

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Represents the number of consecutive periods for which interest payments may be deferred.

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Represents the number of times interest payments may be deferred.

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Represents the period prior to the final repayment date before which the debt instrument cannot be repaid, redeemed, repurchased or defeased.

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Represents the period of each repayment date extension increment.

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Represents the maximum percentage points added to the reference rate to compute the variable rate on the financial instrument, in the event the auction process does not attract sufficient clearing bids.

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The reference rate for the variable rate for income distributions on the financial instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

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Represents the number of custodial trusts with whom the entity entered into put agreements.

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Line of Credit Facility, Interest Rate at Period End as Percentage of Federal Rate

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Related Party Transaction, Maximum Borrowing Capacity

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Fair value of the amount outstanding under the credit facility.

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The amount for notes payable (written promise to pay), due to related parties.

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The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

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The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

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Amount that would be paid, determined under the conditions specified in the contract, if the holder of the share has the right to redeem the shares.

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The maximum amount that the issuer could be required to pay to redeem the instrument by physical settlement, if applicable.

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Long-Term Debt and Credit Facilities - Narrative (Details)							1 Months Ended	12 Months Ended
	Oct. 01, 2019 USD ($)	Jun. 20, 2014 USD ($)	Apr. 07, 2008	Dec. 20, 2006 USD ($)	Nov. 22, 2006 USD ($) period	May 18, 2004 USD ($)	Jun. 30, 2003	Dec. 31, 2019 USD ($) extension	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Oct. 25, 2013 USD ($)	Dec. 31, 2012 USD ($)	Apr. 08, 2005 USD ($) Trust	Jul. 31, 2003 USD ($)	Nov. 26, 2002 USD ($)	Dec. 19, 2001 USD ($)
Debt Instrument [Line Items]
Aggregate principal amount								$ 1,453,000,000	$ 1,457,000,000
AGC Trust Preferred Securities [Member]
Debt Instrument [Line Items]
Basis points			2.50%
AGM Trust Preferred Securities [Member]
Debt Instrument [Line Items]
Basis points							2.00%
AGUS [Member]
Debt Instrument [Line Items]
Aggregate principal amount								1,140,000,000	900,000,000
AGM and AGC [Member] \| AGM CPS securities [Member]
Debt Instrument [Line Items]
Maximum stock purchase obligation of each custodial trust													$ 200,000,000
Number of custodial trusts \| Trust													4,000
Aggregate maximum stock purchase obligation of the custodial trusts													$ 50,000,000
AGM [Member]
Debt Instrument [Line Items]
Aggregate principal amount								4,000,000	5,000,000
AGM [Member] \| AGM CPS securities [Member]
Debt Instrument [Line Items]
Rate basis for income distributions							one-month LIBOR
AGC [Member] \| AGM CPS securities [Member]
Debt Instrument [Line Items]
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]
Interest rate of debt (as a percent)					6.40%
Aggregate principal amount					$ 300,000,000			$ 300,000,000	300,000,000
Interest rate, added to base rate (as a percent)					2.215%
Number of times repayment date may be extended \| extension								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] \| 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								$ 4,000,000	5,000,000
5.6% Notes [Member] \| Notes Payable, Other Payables [Member] \| AGMH [Member]
Debt Instrument [Line Items]
Interest rate of debt (as a percent)								560.00%
Aggregate principal amount								$ 100,000,000	100,000,000					$ 100,000,000
6.25% Notes [Member] \| Notes Payable, Other Payables [Member] \| AGMH [Member]
Debt Instrument [Line Items]
Interest rate of debt (as a percent)								625.00%
Aggregate principal amount								$ 230,000,000	230,000,000						$ 230,000,000
6.875% QUIBS [Member] \| Corporate securities [Member] \| AGMH [Member]
Debt Instrument [Line Items]
Interest rate of debt (as a percent)								6.875%
Aggregate principal amount								$ 100,000,000	100,000,000							$ 100,000,000
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 \| period					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
7% Senior Notes [Member] \| Senior Notes [Member] \| AGUS [Member]
Debt Instrument [Line Items]
Interest rate of debt (as a percent)								7.00%
Aggregate principal amount						$ 200,000,000		$ 200,000,000	200,000,000
Net proceeds from issuance of debt						$ 197,000,000
Effective interest rate of debt (as a percent)								6.40%
5% Senior Notes [Member] \| Senior Notes [Member] \| AGUS [Member]
Debt Instrument [Line Items]
Interest rate of debt (as a percent)								5.00%
Aggregate principal amount		$ 500,000,000						$ 500,000,000	500,000,000
Net proceeds from issuance of debt		$ 495,000,000
Intercompany Loans Payable [Member] \| Line of Credit [Member] \| Revolving Credit Facility [Member] \| Wilbur L. Ross [Member] \| Assured Guaranty LTD [Member]
Debt Instrument [Line Items]
Related party, maximum borrowing capacity											$ 225,000,000
Amounts currently outstanding								0
MAC [Member] \| AGUS [Member]
Debt Instrument [Line Items]
Repayments of Debt								10,000,000	$ 10,000,000	$ 10,000,000
Long-term Debt								$ 40,000,000				$ 90,000,000
AGM, AGC and MAC [Member] \| BlueMountain Capital Management, LLC [Member]
Debt Instrument [Line Items]
Debt Instrument, term	10 years
Interest rate of debt (as a percent)	3.50%
Aggregate principal amount	$ 250,000,000
Annual percent repayment of principal years six through nine	20.00%
Annual percent repayment of principal year ten	20.00%