Changes in Loss and LAE Reserves

No definition available.

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- Definition

Loss And Loss Adjustment Expense Reserves [Line Items]

+ References

No definition available.

+ Details

Name:	mbi_LossAndLossAdjustmentExpenseReservesLineItems
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- Definition

This element represents the weighted average risk free rate used to discount the claim liability related to financial guarantee insurance contracts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 9
-Subparagraph (a)(1)
-URI https://asc.fasb.org/extlink&oid=99382878&loc=SL5749324-161292

+ Details

Name:	us-gaap_FinancialGuaranteeInsuranceContractsClaimLiabilityWeightedAverageRiskFreeDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (cc)
-URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, after effects of policies assumed or ceded, of expense related to the provision for policy benefits and costs incurred.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.5)
-URI https://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 50
-Paragraph 3
-URI https://asc.fasb.org/extlink&oid=99397103&loc=d3e6811-158387

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	mbi_ClaimLiabilityAxis=mbi_LaeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loss And Loss Adjustment Expense Reserves (Loss And LAE Activity) (Narrative) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Loss And Loss Adjustment Expense Reserves [Line Items]
Weighted average risk-free rate used to discount claim liability			3.19%
Lae [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Losses and loss adjustment	$ 17	$ 1,000	$ 5,000	$ 13,000
Loss and loss adjustment expense reserves	$ 20,000		$ 20,000		$ 38,000
Changes in Loss and LAE Reserves			one-year