| **Consolidated Property Casualty Loss And Loss Expense Reserves (Details) - USD ($) $ in Millions** | 12 Months Ended |
|-----------------------------------------------------------------------------------------------------|-----------------|
||
| **Business Acquisition**                                                                            |            |   |   |
| Gross loss and loss expense reserves, January 1                                                     | $ 7,229         | $ 6,677 | $ 6,088 |
| Less reinsurance recoverable                                                                        | 327             | 277 | 342 |
| Net loss and loss expense reserves, January 1                                                       | 6,902           | 6,400 | 5,746 |
| **Net incurred loss and loss expenses related to:**                                                 |            |   |   |
| Current accident year                                                                               | 4,875           | 4,024 | 3,968 |
| Prior accident years                                                                                | (159)           | (428) | (131) |
| Total incurred                                                                                      | 4,716           | 3,596 | 3,837 |
| **Net paid loss and loss expenses related to:**                                                     |            |   |   |
| Current accident year                                                                               | 1,592           | 1,379 | 1,493 |
| Prior accident years                                                                                | 2,095           | 1,715 | 1,690 |
| Total paid                                                                                          | 3,687           | 3,094 | 3,183 |
| Net loss and loss expense reserves, December 31                                                     | 7,931           | 6,902 | 6,400 |
| Plus reinsurance recoverable                                                                        | 405             | 327 | 277 |
| Gross loss and loss expense reserves, December 31                                                   | $ 8,336         | $ 7,229 | $ 6,677 |

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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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Net Incurred Loss And Loss Expenses Related To
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Net Paid Loss And Loss Expenses Related To
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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.
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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.
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Amount, after effects of reinsurance, of payments to settle claims incurred in the current period and related claims settlement costs.
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Amount, after effects of reinsurance, of payments to settle claims incurred in prior periods and related claims settlement costs.
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Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred and costs incurred in the claim settlement process.
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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.
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Amount, after effects of reinsurance, of payments to settle insured claims and pay costs incurred in the claims settlement process.
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Amount, after valuation allowance, recoverable under reinsurance contracts for losses reported to the ceding insurer but not yet paid and amounts expected for incurred losses and settlement expenses, which have not yet been reported to the ceding insurer.
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Amount, after effects of reinsurance, of expense for claims incurred in the current reporting period and related claims settlement costs.
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Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs.
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