|**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 31,20222021Direct written premiums$1,703$1,545Assumed written premiums263205Ceded written premiums(67)(57)Net written premiums$1,899$1,693Direct earned premiums$1,561$1,429Assumed earned premiums121101Ceded earned premiums(64)(55)Earned premiums$1,618$1,475Direct incurred loss and loss expenses$895$868Assumed incurred loss and loss expenses7378Ceded incurred loss and loss expenses(12)(23)Incurred loss and loss expenses$956$923
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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 31,20222021Direct earned premiums$90$87Ceded earned premiums(18)(18)Earned premiums$72$69Direct contract holders' benefits incurred114107Ceded contract holders' benefits incurred(31)(27)Contract holders' benefits incurred$83$80                                                                                                                                                                                                                                          
|                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|(Dollars in millions)                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Direct earned premiums                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Ceded earned premiums                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Earned premiums                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Direct contract holders' benefits incurred             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Ceded contract holders' benefits incurred              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Contract holders' benefits incurred                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
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