| **Claim and Claim Adjustment Expense Reserves - Reconciliation of claim and claim adjustment expense reserves (Details) - USD ($) $ in Millions** | 3 Months Ended |
|---------------------------------------------------------------------------------------------------------------------------------------------------|----------------|
||
| **Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]**                                                                      |           |   |
| Gross, beginning of year                                                                                                                          | $ 22,343       | $ 22,663 |
| Ceded, beginning of year                                                                                                                          | 4,094          | 4,087 |
| Net reserves, beginning of year                                                                                                                   | 18,249         | 18,576 |
| **Net incurred claim and claim adjustment expenses:**                                                                                             |           |   |
| Provision for insured events of current year                                                                                                      | 1,207          | 1,224 |
| Decrease in provision for insured events of prior years                                                                                           | (82)           | (45) |
| Amortization of discount                                                                                                                          | 48             | 48 |
| Total net incurred                                                                                                                                | 1,173          | 1,227 |
| **Net payments attributable to:**                                                                                                                 |           |   |
| Current year events                                                                                                                               | (68)           | (76) |
| Prior year events                                                                                                                                 | (1,184)        | (1,147) |
| Total net payments                                                                                                                                | (1,252)        | (1,223) |
| Foreign currency translation adjustment and other                                                                                                 | 14             | 39 |
| Net reserves, end of period                                                                                                                       | 18,184         | 18,619 |
| Ceded reserves, end of year                                                                                                                       | 4,076          | 4,399 |
| Gross reserves, end of year                                                                                                                       | $ 22,260       | $ 23,018 |

| X                                                                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Ceded Claim And Claim Adjustment Expenses
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Liability for Unpaid Claims and Claims Adjustment Expense Foreign CTA and other
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Liability for Unpaid Claims and Claims Adjustment Expense Incurred Claims Amortization of Discount
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Liability for unpaid claim and claim adjustment expense, gross
+ References
No definition available.
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| X                                                                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after effects of reinsurance, of payments to settle claims incurred in the current period and related claims settlement costs.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after effects of reinsurance, of payments to settle claims incurred in prior periods and related claims settlement costs.
+ References
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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
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| X                                                                                                                                                                                                                                                  |
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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
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| - Definition
A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.
+ References
No definition available.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after effects of reinsurance, of payments to settle insured claims and pay costs incurred in the claims settlement process.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after effects of reinsurance, of expense for claims incurred in the current reporting period and related claims settlement costs.
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs.
+ References
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