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Contracts Accounted for as Insurance - Selected Information for Policies Paid In Installments (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2025 | Dec. 31, 2024 | Sep. 30, 2024 | Dec. 31, 2023
Financial Guarantee Insurance Premiums [Line Items] |  |  |  |
Premiums receivable, net of commissions payable | $ 1,583 | $ 1,551 | $ 1,513 | $ 1,468
Financial Guarantee Policies Paid in Installments |  |  |  |
Financial Guarantee Insurance Premiums [Line Items] |  |  |  |
Premiums receivable, net of commissions payable | 1,582 | 1,550 |  |
Deferred premium revenue | $ 1,855 | $ 1,901 |  |
Weighted-average risk-free rate used to discount premiums | 2.60% | 2.50% |  |
Weighted-average period of premiums receivable (in years) | 12 years | 12 years 3 months 18 days |  |

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- Definition [Line Items] for Financial Guarantee Insurance Premiums [Table] + References No definition available. + Details
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- Definition Amount of the premium receivable for financial guarantee insurance contracts reported in the statement of financial position. This element primarily would consist of those financial guarantee insurance contracts which premiums are to be collected over the contract period, but may, on occasion, include premiums which are to be collected in full at inception, but which straddle a financial reporting period. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 310 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (c)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477363/944-310-50-3 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 310 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (c)(5) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477363/944-310-50-3 + Details
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- Definition Weighted average period over which premium receivable for financial guarantee insurance contracts is collected where premium is received over the contract period, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 310 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a)(5) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477363/944-310-50-3 + Details
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- Definition Weighted-average risk-free rate used to discount amount of premium expected to be collected for financial guarantee insurance contract where premium is to be received over contract period. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 310 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a)(4) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477363/944-310-50-3 + Details
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- Definition Amount of unearned premium revenue in the statement of financial position for financial guarantee insurance contracts where the premium is received over the contract period. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 310 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477363/944-310-50-3 + Details
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- Details
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