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Loss and Loss Adjustment Expense Reserves (Schedule of Loss and Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Loss And Loss Adjustment Expense Reserves [Line Items] |  |  |  |  |
Changes in unearned premium revenue | $ 33 |  | $ 34 |  | $ 56
Loss And Lae Reserves [Member] |  |  |  |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |  |  |  |
Gross loss and LAE reserve, beginning balance | 473 | [1] | 439 |  |
Loss payments for cases | (157) |  | (214) |  |
Accretion of claim liability discount | 19 |  | 15 |  |
Changes in discount rates | (19) |  | (4) |  |
Changes in assumptions | 212 | [2] | 235 | [3] |
Changes in unearned premium revenue | (2) |  | 2 |  |
Gross loss and LAE reserve, ending balance | $ 526 | [1] | $ 473 | [1] | $ 439
[1] | Amounts are net of estimated recoveries of expected future claims.
[2] | Includes changes in amount and timing of estimated payments and recoveries.
[3] | includes changes in amount and timing of estimated payments and recoveries.

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- Definition Financial Guarantee Insurance Contracts Claim Liability Significant Components Of Change In Assumptions + References No definition available. + Details
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- Definition Loss And Loss Adjustment Expense Reserves [Line Items] + References No definition available. + Details
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- Definition This element represents the amount of the change in the claim liability related to financial guarantee insurance contracts arising from the accretion of the discount of the claim liability. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Subparagraph (a)(4) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-9 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Subparagraph (a)(2)(ii) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-9 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Subparagraph (a)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-9 + Details
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- Definition This element represents the amount of change in the claim liability related to financial guarantee insurance contracts arising from a change in the rate used to discount the claim liability. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Subparagraph (a)(4) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-9 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Subparagraph (a)(2)(i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-9 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Subparagraph (a)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-9 + Details
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- Definition Amount of increase (decrease) unearned premiums written. Excludes portion of unearned premiums amortized into income. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (a) -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-28 + Details
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- 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://www.xbrl.org/2003/role/exampleRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 55 -Paragraph 7 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480046/944-40-55-7 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 55 -Paragraph 9E -Publisher FASB -URI https://asc.fasb.org/1943274/2147480046/944-40-55-9E Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (cc) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-3 Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(13)(a)(1)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1 + Details
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- Details
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