Insurance Contracts Financial Guarantee Insurance Contracts - Summary of Percentage Ceded to Reinsurers and Reinsurance Recoverable and Rating Levels (Details) $ in Millions	Mar. 31, 2021 USD ($)
Insurance [Abstract]
Ceded Loss And Loss Expenses Paid Not Yet Recovered	$ 0

Ceded Loss And Loss Expenses Paid Not Yet Recovered

No definition available.

Name:	ambc_CededLossAndLossExpensesPaidNotYetRecovered
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant