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Business Developments And Risks And Uncertainties (Narrative) (Detail) $ in Millions |  | 3 Months Ended
--- | --- | ---
Jan. 01, 2025 USD ($) | Mar. 31, 2025 USD ($) Segments
Business Acquisition [Line Items] |  |
Number of operating segments | Segments |  | 3
MBIA Mexico [Member] |  |
Business Acquisition [Line Items] |  |
Capital returned by subsidiary |  | $ 12
Puerto Rico Electric Power Authority [Member] |  |
Business Acquisition [Line Items] |  |
Outstanding insured bonds |  | $ 657
National Public Finance Guarantee Corporation [Member] | Puerto Rico Electric Power Authority [Member] |  |
Business Acquisition [Line Items] |  |
Claims payments | $ 13 |

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- 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 Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 805 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479907/805-20-50-5 + Details
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- Definition Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 49 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482785/280-10-55-49 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482810/280-10-50-18 + Details
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