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Loss and Loss Adjustment Expense Reserves (Loss and LAE Activity) (Narrative) (Detail) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2024 | Mar. 31, 2023 | Dec. 31, 2023
Loss And Loss Adjustment Expense Reserves [Line Items] |  |  |
Weighted average risk-free rates used to discount claim liability | 4.33% |  | 3.97%
Lae [Member] |  |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |  |
Losses and loss adjustment | $ 2 | $ 2 |
Loss and loss adjustment expense reserves | $ 8 |  | $ 8
Changes in Loss and LAE Reserves | one-year |  |

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- Definition Changes in Loss and LAE Reserves + 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 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 -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 9 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-9 + 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://fasb.org/us-gaap/role/ref/legacyRef -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 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
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Balance Type: | credit
Period Type: | instant

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- 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://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(5)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1 + Details
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- Details
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