Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Detail) $ in Millions	Dec. 31, 2021 USD ($)
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	$ 1,751
Changes recognized
Discounted RMBS subrogation (gross of reinsurance), ending balance	$ 1,730

This element represents the reduction to gross claim liability for subrogation on insured RMBS financial obligations with credit deterioration.

No definition available.

Name:	ambc_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityRmbsSubrogation
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant