Label	Element	Value
Reinsurance of SGI Insured Portfolio [Member] | Structured Finance [Member]
Guarantor Obligations, Net Expected Loss to be Paid After Recoveries for Representations and Warranties	ago_GuarantorObligationsNetExpectedLosstobePaidAfterRecoveriesforRepresentationsandWarranties	$ 130,000,000
Reinsurance of SGI Insured Portfolio [Member] | Other Structured Finance [Member]
Guarantor Obligations, Net Expected Loss to be Paid After Recoveries for Representations and Warranties	ago_GuarantorObligationsNetExpectedLosstobePaidAfterRecoveriesforRepresentationsandWarranties	0
Reinsurance of SGI Insured Portfolio [Member] | Public Finance [Member]
Guarantor Obligations, Net Expected Loss to be Paid After Recoveries for Representations and Warranties	ago_GuarantorObligationsNetExpectedLosstobePaidAfterRecoveriesforRepresentationsandWarranties	1,000,000
Non-US [Member] | Reinsurance of SGI Insured Portfolio [Member] | Public Finance [Member]
Guarantor Obligations, Net Expected Loss to be Paid After Recoveries for Representations and Warranties	ago_GuarantorObligationsNetExpectedLosstobePaidAfterRecoveriesforRepresentationsandWarranties	1,000,000
UNITED STATES | Reinsurance of SGI Insured Portfolio [Member] | Residential Mortgage Backed Securities [Member]
Guarantor Obligations, Net Expected Loss to be Paid After Recoveries for Representations and Warranties	ago_GuarantorObligationsNetExpectedLosstobePaidAfterRecoveriesforRepresentationsandWarranties	130,000,000
UNITED STATES | Reinsurance of SGI Insured Portfolio [Member] | Public Finance [Member]
Guarantor Obligations, Net Expected Loss to be Paid After Recoveries for Representations and Warranties	ago_GuarantorObligationsNetExpectedLosstobePaidAfterRecoveriesforRepresentationsandWarranties	0
Accounting Standards Update 2016-01 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 32,000,000