| **Segment Information (Detail) - USD ($) $ in Millions**               | 3 Months Ended | 9 Months Ended |         |
|------------------------------------------------------------------------|----------------|----------------|---------|
||
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Earned premiums                                                        | $ 1,882        | $ 1,669        | $ 5,345 | $ 4,806 |   |
| Fee revenues                                                           | 5              | 4              | 12      | 11 |   |
| Other revenues                                                         | 2              | 3              | 7       | 8 |   |
| Investment income, net of expenses                                     | 193            | 179            | 573     | 528 |   |
| Investment gains and losses, net                                       | (674)          | (70)           | (2,494) | 954 |   |
| Total revenues                                                         | 1,408          | 1,785          | 3,443   | 6,307 |   |
| Income before Income Taxes                                             | (579)          | 184            | (1,980) | 1,824 |   |
| Identifiable Assets                                                    | 28,199         |           | 28,199  |   | $ 31,387 |
| Consolidated Property And Casualty Insurance                           |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Earned premiums                                                        | 1,809          | 1,596          | 5,124   | 4,585 |   |
| Identifiable Assets                                                    | 5,072          |           | 5,072   |   | 4,421 |
| Life Insurance Segment                                                 |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Identifiable Assets                                                    | 1,525          |           | 1,525   |   | 1,590 |
| Investment Segment                                                     |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Identifiable Assets                                                    | 20,726         |           | 20,726  |   | 24,481 |
| Corporate and Other                                                    |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Identifiable Assets                                                    | 876            |           | 876     |   | $ 895 |
| Operating Segments | Commercial Insurance                              |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Earned premiums                                                        | 1,028          | 930            | 2,984   | 2,727 |   |
| Fee revenues                                                           | 1              | 1              | 3       | 3 |   |
| Total revenues                                                         | 1,029          | 931            | 2,987   | 2,730 |   |
| Income Before Income Taxes                                             | 11             | 182            | 25      | 457 |   |
| Operating Segments | Commercial Insurance | Commercial Casualty Line   |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Earned premiums                                                        | 360            | 323            | 1,046   | 938 |   |
| Operating Segments | Commercial Insurance | Commercial Property Line   |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Earned premiums                                                        | 292            | 264            | 846     | 776 |   |
| Operating Segments | Commercial Insurance | Commercial Auto Line       |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Earned premiums                                                        | 213            | 200            | 627     | 591 |   |
| Operating Segments | Commercial Insurance | Workers' Compensation Line |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Earned premiums                                                        | 73             | 66             | 209     | 201 |   |
| Operating Segments | Commercial Insurance | Other Commercial Lines     |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Earned premiums                                                        | 90             | 77             | 256     | 221 |   |
| Operating Segments | Personal Insurance                                |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Earned premiums                                                        | 431            | 388            | 1,246   | 1,146 |   |
| Fee revenues                                                           | 1              | 1              | 3       | 3 |   |
| Total revenues                                                         | 432            | 389            | 1,249   | 1,149 |   |
| Income Before Income Taxes                                             | (18)           | (10)           | (2)     | 16 |   |
| Operating Segments | Personal Insurance | Personal Auto                |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Earned premiums                                                        | 158            | 153            | 465     | 457 |   |
| Operating Segments | Personal Insurance | Home Owner Line              |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Earned premiums                                                        | 213            | 184            | 609     | 536 |   |
| Operating Segments | Personal Insurance | Other Personal Lines         |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Earned premiums                                                        | 60             | 51             | 172     | 153 |   |
| Operating Segments | Excess and Surplus Lines Insurance                |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Earned premiums                                                        | 125            | 105            | 361     | 289 |   |
| Fee revenues                                                           | 1              | 1              | 2       | 2 |   |
| Total revenues                                                         | 126            | 106            | 363     | 291 |   |
| Income Before Income Taxes                                             | 9              | 7              | 44      | 25 |   |
| Operating Segments | Life Insurance Segment                            |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Earned premiums                                                        | 73             | 73             | 221     | 221 |   |
| Fee revenues                                                           | 2              | 1              | 4       | 3 |   |
| Total revenues                                                         | 75             | 74             | 225     | 224 |   |
| Income Before Income Taxes                                             | 11             | (5)            | 22      | (9) |   |
| Operating Segments | Investment Segment                                |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Investment income, net of expenses                                     | 193            | 179            | 573     | 528 |   |
| Investment gains and losses, net                                       | (674)          | (70)           | (2,494) | 954 |   |
| Total revenues                                                         | (481)          | 109            | (1,921) | 1,482 |   |
| Income Before Income Taxes                                             | (508)          | 83             | (2,003) | 1,403 |   |
| Corporate, Non-Segment                                                 |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Total revenues                                                         | 227            | 176            | 540     | 431 |   |
| Corporate, Non-Segment | Reinsurance assumed and other non segment     |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Earned premiums                                                        | 225            | 173            | 533     | 423 |   |
| Corporate, Non-Segment | Corporate and Other                           |           |           |    |   |   |
| **Segment Reporting Information**                                      |           |           |    |   |   |
| Other revenues                                                         | 2              | 3              | 7       | 8 |   |
| Income Before Income Taxes                                             | $ (84)         | $ (73)         | $ (66)  | $ (68) |   |

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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------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Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.
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Amount of realized and unrealized gain (loss) on investment.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.
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| - Definition
Income from agency and brokerage operations (includes sales of annuities and supplemental contracts); service charges, commissions, and fees from the sale of insurance and related services; and management fees from separate accounts, deferred annuities, and universal life products.
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| - Definition
Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.
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Amount of revenue and income classified as other.
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned.
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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).
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