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Insurance Contracts - Summary of Loss Reserve Roll-Forward, Net of Subrogation Recoverable and Reinsurance (Details) - USD ($) $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2024 | Mar. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2022
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Beginning balance of net loss and loss expense reserves | $ 570 | $ 419 |  |
Current Year Claims and Claims Adjustment Expense | 18 | 2 |  |
Prior Year Claims and Claims Adjustment Expense | (19) | 16 |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims | (1) | 18 |  |
Claim and loss expense payments, net of subrogation and reinsurance | (1) | 0 |  |
Claim and loss expense (payments) recoveries, net of subrogation and reinsurance | (55) | 141 |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid | 56 | (141) |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Foreign Currency Translation Gain (Loss) | 0 | 0 |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 513 | 578 | $ 570 | $ 419
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 208 | 127 | 186 | 115
Policyholder Benefits and Claims Incurred, Ceded | 35 | 20 |  |
Ceded Loss And Loss Expenses Paid Not Yet Recovered |  | 3 |  |
Liability for Claim and Claim Adjustment Expenses Net of Subrogation recoverables | 721 | $ 705 | 756 | $ 534
Financial Guarantee |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] |  |  |  |
Ceded Loss And Loss Expenses Paid Not Yet Recovered | 1 |  | (1) |
Loss Reserves Ceded To Reinsurers | $ 26 |  | $ 30 |

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- Definition Amount, after effects of reinsurance, of payments to settle claims incurred in the current period and related claims settlement costs. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (c) -SubTopic 40 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
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- Definition Amount, after effects of reinsurance, of payments to settle claims incurred in prior periods and related claims settlement costs. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (c) -SubTopic 40 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
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- Definition Amount of foreign currency gain (loss) which decreases (increases) the cost of settling unpaid claims after deduction of reinsurance recoveries. Includes, but is not limited to, claims which have been incurred but not reported. + References No definition available. + Details
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- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred and costs incurred in the claim settlement process. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
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- Definition Liability as of the balance sheet date for amounts representing estimated cost of settling unpaid claims under the terms of the underlying insurance policies, less estimated reinsurance recoveries on such claims. This includes an estimate for claims which have been incurred but not reported. Claim adjustment expenses represent the costs estimated to be incurred in the settlement of unpaid claims. + References Reference 1: 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//1943274/2147479440/944-210-S99-1 Reference 2: 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 3: 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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