|**Reinsurance (Tables)**                               | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|------------------------------------------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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|**Reinsurance Disclosures [Abstract]**                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Property Casualty Insurance Assumed And Ceded Business | The table below summarizes our consolidated property casualty insurance net written premiums, earned premiums and incurred loss and loss expenses:(Dollars in millions)Three months ended March 31,20242023Direct written premiums$2,125$1,859Assumed written premiums239244Ceded written premiums(116)(84)Net written premiums$2,248$2,019Direct earned premiums$1,934$1,760Assumed earned premiums152159Ceded earned premiums(94)(78)Earned premiums$1,992$1,841Direct incurred loss and loss expenses$1,193$1,299Assumed incurred loss and loss expenses7676Ceded incurred loss and loss expenses1(58)Incurred loss and loss expenses$1,270$1,317
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|(Dollars in millions)                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Direct written premiums                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Assumed written premiums                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Ceded written premiums                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Net written premiums                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Direct earned premiums                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Assumed earned premiums                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Ceded earned premiums                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Earned premiums                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Direct incurred loss and loss expenses                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Assumed incurred loss and loss expenses                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Ceded incurred loss and loss expenses                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Incurred loss and loss expenses                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Life Insurance Assumed and Ceded Business              | The table below summarizes our consolidated life insurance earned premiums and contract holders' benefits incurred:(Dollars in millions)Three months ended March 31,20242023Direct earned premiums$99$96Ceded earned premiums(20)(19)Earned premiums$79$77Direct contract holders' benefits incurred9497Ceded contract holders' benefits incurred(15)(16)Contract holders' benefits incurred$79$81                                                                                                                                                                                                                                                  
|                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|(Dollars in millions)                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Direct earned premiums                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Ceded earned premiums                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Earned premiums                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
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|Direct contract holders' benefits incurred             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Ceded contract holders' benefits incurred              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Contract holders' benefits incurred                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
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