XML 79 R61.htm IDEA: XBRL DOCUMENT v3.21.1

Fair Value Measurements - Summary of Changes in Level 3 Fair Value Category (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($) level3FinancialInstruments	Mar. 31, 2020 USD ($) level3FinancialInstruments	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis Asset or Liability, Transfers into or out of Level 3 | level3FinancialInstruments	0	0
Interest Rate Swap [Member] | Interest Rate Swap [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	$ 66	$ 79	$ 85	$ 67
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	(17)	13
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	(17)	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	(17)	13
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(2)	(1)
Credit Derivative [Member] | Credit Derivative [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	0	(2)	0	0
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	0	(2)
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	0	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	(1)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	0
Derivative [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	65	77	84	66
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	(17)	12
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	(17)	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	(17)	12
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(2)	(1)
Level 3 [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	6,194	5,884	6,376	6,207
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	(145)	130
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	49	(377)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	(145)	130
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	49	(377)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(86)	(76)
Level 3 [Member] | Loans Receivable [Member] | Loans [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	2,948	2,932	2,998	3,108
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	9	88
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	24	(190)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	9	88
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	24	(190)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(84)	(74)
Level 3 [Member] | Investments [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	76	66	78	72
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	(2)	(6)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	(2)	(6)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	0	0
Level 3 [Member] | Other Assets [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	1	3	1	3
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	0	0
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	0	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	0	0
Level 3 [Member] | Derivative Financial Instruments, Liabilities [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	65	77	84	66
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	(17)	12
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	0	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	(17)	12
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements	(2)	(1)
Level 3 [Member] | Corporate Debt Securities [Member] | Investment Contracts [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability	3,103	2,806	$ 3,215	$ 2,957
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss)	(138)	30
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	26	(181)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings	(138)	30
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss	$ 26	$ (181)

X

- Definition

Fair value measurement with unobservable inputs reconciliation recurring basis asset or liability.

+ References

No definition available.

+ Details

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

X

- Definition

Amount of gain or loss included in earnings arising from financial instruments measured on a recurring basis using unobservable inputs.

+ References

No definition available.

+ Details

Name:	ambc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetOrLiabilityGainLossIncludedInEarnings
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of gain or loss included in other comprehensive income arising from financial instruments measured on a recurring basis using unobservable inputs.

+ References

No definition available.

+ Details

Name:	ambc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetOrLiabilityGainLossIncludedInOtherComprehensiveIncomeLoss
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of issuances related to financial instruments measured on a recurring basis using unobservable inputs.

+ References

No definition available.

+ Details

Name:	ambc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetOrLiabilityIssues
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of purchases of financial instruments measured on a recurring basis using unobservable inputs.

+ References

No definition available.

+ Details

Name:	ambc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetOrLiabilityPurchases
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of sales of financial instruments measured on a recurring basis using unobservable inputs.

+ References

No definition available.

+ Details

Name:	ambc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetOrLiabilitySales
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Amount of settlements related to financial instruments measured on a recurring basis using unobservable inputs.

+ References

No definition available.

+ Details

Name:	ambc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetOrLiabilitySettlements
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis Asset or Liability, Transfers into or out of Level 3

+ References

No definition available.

+ Details

Name:	ambc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetOrLiabilityTransfersIntoOrOutOfLevel3
Namespace Prefix:	ambc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of unrealized gain (loss) recognized in income from asset (liability) measured at fair value on recurring basis using unobservable input (level 3) and still held.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueAssetLiabilityRecurringBasisStillHeldUnrealizedGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of unrealized gain (loss) recognized in other comprehensive income (OCI) from asset (liability) measured at fair value on recurring basis using unobservable input (level 3) and still held.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueAssetLiabilityRecurringBasisStillHeldUnrealizedGainLossOci
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

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.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=ambc_CreditDerivativeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=ambc_CreditDerivativeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_DerivativeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_LoansReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=us-gaap_LoanOriginationCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ConsolidatedEntitiesAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_InvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_OtherAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=us-gaap_InvestmentContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: