| **Supplementary Insurance Information (Details) - USD ($) $ in Millions** | 12 Months Ended |
|---------------------------------------------------------------------------|-----------------|
||
| **Supplementary Insurance Information, by Segment**                       |            |   |   |
| Deferred policy acquisition costs                                         | $ 774           | $ 738 | $ 670 |
| Gross future policy benefits, losses, claims and expense losses           | 8,947           | 8,448 | 7,972 |
| Gross unearned premium                                                    | 2,788           | 2,516 | 2,404 |
| Other policy claims and benefits payable                                  | 35              | 38 | 30 |
| Earned premiums                                                           | 5,604           | 5,170 | 4,954 |
| Investment income, net of expenses                                        | 571             | 554 | 547 |
| Benefits, claims losses and settlement expense                            | 3,638           | 3,490 | 3,390 |
| Amortization of deferred policy acquisition costs                         | 1,034           | 946 | 913 |
| Underwriting, acquisition and insurance expenses                          | 704             | 651 | 633 |
| Net written premiums                                                      | 5,518           | 5,033 | 4,843 |
| Commercial Insurance                                                      |            |   |   |
| **Supplementary Insurance Information, by Segment**                       |            |   |   |
| Deferred policy acquisition costs                                         | 311             | 291 | 284 |
| Gross future policy benefits, losses, claims and expense losses           | 4,569           | 4,466 | 4,236 |
| Gross unearned premium                                                    | 1,665           | 1,576 | 1,548 |
| Earned premiums                                                           | 3,319           | 3,218 | 3,165 |
| Benefits, claims losses and settlement expense                            | 2,030           | 2,049 | 2,042 |
| Amortization of deferred policy acquisition costs                         | 631             | 608 | 590 |
| Underwriting, acquisition and insurance expenses                          | 422             | 415 | 419 |
| Net written premiums                                                      | 3,410           | 3,245 | 3,202 |
| Personal Insurance                                                        |            |   |   |
| **Supplementary Insurance Information, by Segment**                       |            |   |   |
| Deferred policy acquisition costs                                         | 130             | 126 | 121 |
| Gross future policy benefits, losses, claims and expense losses           | 687             | 679 | 587 |
| Gross unearned premium                                                    | 757             | 725 | 683 |
| Earned premiums                                                           | 1,404           | 1,336 | 1,241 |
| Benefits, claims losses and settlement expense                            | 985             | 972 | 918 |
| Amortization of deferred policy acquisition costs                         | 251             | 242 | 225 |
| Underwriting, acquisition and insurance expenses                          | 164             | 147 | 135 |
| Net written premiums                                                      | 1,435           | 1,378 | 1,294 |
| Excess and Surplus Lines Insurance                                        |            |   |   |
| **Supplementary Insurance Information, by Segment**                       |            |   |   |
| Deferred policy acquisition costs                                         | 25              | 21 | 17 |
| Gross future policy benefits, losses, claims and expense losses           | 351             | 298 | 264 |
| Gross unearned premium                                                    | 152             | 123 | 105 |
| Earned premiums                                                           | 278             | 234 | 209 |
| Benefits, claims losses and settlement expense                            | 142             | 104 | 86 |
| Amortization of deferred policy acquisition costs                         | 47              | 39 | 35 |
| Underwriting, acquisition and insurance expenses                          | 38              | 29 | 28 |
| Net written premiums                                                      | 303             | 249 | 219 |
| Reinsurance assumed and other non segment                                 |            |   |   |
| **Supplementary Insurance Information, by Segment**                       |            |   |   |
| Deferred policy acquisition costs                                         | 46              | 26 | 16 |
| Gross future policy benefits, losses, claims and expense losses           | 481             | 203 | 132 |
| Gross unearned premium                                                    | 213             | 91 | 67 |
| Earned premiums                                                           | 333             | 132 | 107 |
| Benefits, claims losses and settlement expense                            | 195             | 98 | 92 |
| Amortization of deferred policy acquisition costs                         | 57              | 18 | 17 |
| Underwriting, acquisition and insurance expenses                          | 42              | 24 | 18 |
| Net written premiums                                                      | 368             | 158 | 125 |
| Property, Liability and Casualty Insurance Product Line                   |            |   |   |
| **Supplementary Insurance Information, by Segment**                       |            |   |   |
| Deferred policy acquisition costs                                         | 512             | 464 | 438 |
| Gross future policy benefits, losses, claims and expense losses           | 6,088           | 5,646 | 5,219 |
| Gross unearned premium                                                    | 2,787           | 2,515 | 2,403 |
| Earned premiums                                                           | 5,334           | 4,920 | 4,722 |
| Investment income, net of expenses                                        | 419             | 401 | 392 |
| Benefits, claims losses and settlement expense                            | 3,352           | 3,223 | 3,138 |
| Amortization of deferred policy acquisition costs                         | 986             | 907 | 867 |
| Underwriting, acquisition and insurance expenses                          | 666             | 615 | 600 |
| Net written premiums                                                      | 5,516           | 5,030 | 4,840 |
| Accident Health Insurance Segment                                         |            |   |   |
| **Supplementary Insurance Information, by Segment**                       |            |   |   |
| Net written premiums                                                      | 2               | 3 | 3 |
| Life Insurance Segment                                                    |            |   |   |
| **Supplementary Insurance Information, by Segment**                       |            |   |   |
| Deferred policy acquisition costs                                         | 262             | 274 | 232 |
| Gross future policy benefits, losses, claims and expense losses           | 2,859           | 2,802 | 2,753 |
| Gross unearned premium                                                    | 1               | 1 | 1 |
| Other policy claims and benefits payable                                  | 35              | 38 | 30 |
| Earned premiums                                                           | 270             | 250 | 232 |
| Investment income, net of expenses                                        | 152             | 153 | 155 |
| Benefits, claims losses and settlement expense                            | 286             | 267 | 252 |
| Amortization of deferred policy acquisition costs                         | 48              | 39 | 46 |
| Underwriting, acquisition and insurance expenses                          | $ 38            | $ 36 | $ 33 |

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Amount of amortization of deferred policy acquisition cost recognized, as disclosed in supplementary insurance information.
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Amount of insurance benefit, claim, loss and settlement expenses incurred, as disclosed in supplementary insurance information.
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Amount of deferred policy acquisition cost capitalized on contract remaining in force, as disclosed in supplementary insurance information.
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Amount of reserve for future policy claim payable and loss expense to be incurred, disclosed in supplementary insurance information.
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Amount of net investment income earned, disclosed in supplementary insurance information.
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Amount of operating expense classified as other, disclosed in supplementary insurance information.
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Amount of claim and benefit payable classified as other, disclosed in supplementary insurance information.
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Amount of premium revenue earned, disclosed in supplementary insurance information.
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Amount, after premiums ceded and assumed, of premium written, disclosed in supplementary insurance information.
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Amount of premium not yet earned, disclosed in supplementary insurance information.
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