| **Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions** | 3 Months Ended | 9 Months Ended |
|----------------------------------------------------------------------------------------|----------------|----------------|
||
| **Operating Revenues**                                                                 |           |           |   |   |
| Net earned premiums                                                                    | $ 1,767        | $ 1,751        | $ 5,196 | $ 5,173 |
| Net investment income                                                                  | 524            | 354            | 1,461 | 1,412 |
| Other revenues                                                                         | 96             | 97             | 293 | 286 |
| Total operating revenues                                                               | 2,387          | 2,202          | 6,950 | 6,871 |
| **Claims, Benefits and Expenses**                                                      |           |           |   |   |
| Net incurred claims and benefits                                                       | 1,195          | 1,198          | 3,934 | 3,999 |
| Policyholders' dividends                                                               | 7              | 2              | 15 | 9 |
| Amortization of deferred acquisition costs                                             | 314            | 319            | 926 | 936 |
| Other insurance related expenses                                                       | 295            | 263            | 842 | 790 |
| Other expenses                                                                         | 147            | 138            | 439 | 388 |
| Total claims, benefits and expenses                                                    | 1,958          | 1,920          | 6,156 | 6,122 |
| Operating income (loss) before income tax                                              | 429            | 282            | 794 | 749 |
| Income tax (expense) benefit on operating income (loss)                                | (118)          | (72)           | (191) | (182) |
| Net operating income (loss)                                                            | 311            | 210            | 603 | 567 |
| Net realized investment gains (losses), pre-tax                                        | 46             | (49)           | 26 | (39) |
| Income tax (expense) benefit on net realized investment gains (losses)                 | (14)           | 17             | (11) | 21 |
| Net realized investment gains (losses), after tax                                      | 32             | (32)           | 15 | (18) |
| Net Income (Loss)                                                                      | 343            | 178            | 618 | 549 |
| Specialty [Member]                                                                     |           |           |   |   |
| **Operating Revenues**                                                                 |           |           |   |   |
| Net earned premiums                                                                    | 704            | 706            | 2,088 | 2,075 |
| Net investment income                                                                  | 140            | 76             | 380 | 365 |
| Other revenues                                                                         | 93             | 86             | 269 | 245 |
| Total operating revenues                                                               | 937            | 868            | 2,737 | 2,685 |
| **Claims, Benefits and Expenses**                                                      |           |           |   |   |
| Net incurred claims and benefits                                                       | 330            | 307            | 1,097 | 1,152 |
| Policyholders' dividends                                                               | 4              | 1              | 6 | 3 |
| Amortization of deferred acquisition costs                                             | 151            | 150            | 443 | 440 |
| Other insurance related expenses                                                       | 77             | 67             | 225 | 202 |
| Other expenses                                                                         | 78             | 73             | 232 | 209 |
| Total claims, benefits and expenses                                                    | 640            | 598            | 2,003 | 2,006 |
| Operating income (loss) before income tax                                              | 297            | 270            | 734 | 679 |
| Income tax (expense) benefit on operating income (loss)                                | (102)          | (91)           | (248) | (228) |
| Net operating income (loss)                                                            | 195            | 179            | 486 | 451 |
| Net realized investment gains (losses), pre-tax                                        | 9              | (22)           | 2 | (18) |
| Income tax (expense) benefit on net realized investment gains (losses)                 | (3)            | 8              | (1) | 7 |
| Net realized investment gains (losses), after tax                                      | 6              | (14)           | 1 | (11) |
| Net Income (Loss)                                                                      | 201            | 165            | 487 | 440 |
| Commercial [Member]                                                                    |           |           |   |   |
| **Operating Revenues**                                                                 |           |           |   |   |
| Net earned premiums                                                                    | 719            | 705            | 2,103 | 2,086 |
| Net investment income                                                                  | 175            | 82             | 465 | 455 |
| Other revenues                                                                         | 7              | 9              | 21 | 27 |
| Total operating revenues                                                               | 901            | 796            | 2,589 | 2,568 |
| **Claims, Benefits and Expenses**                                                      |           |           |   |   |
| Net incurred claims and benefits                                                       | 446            | 427            | 1,357 | 1,388 |
| Policyholders' dividends                                                               | 3              | 1              | 9 | 6 |
| Amortization of deferred acquisition costs                                             | 118            | 118            | 351 | 352 |
| Other insurance related expenses                                                       | 151            | 128            | 422 | 385 |
| Other expenses                                                                         | 9              | 10             | 25 | 23 |
| Total claims, benefits and expenses                                                    | 727            | 684            | 2,164 | 2,154 |
| Operating income (loss) before income tax                                              | 174            | 112            | 425 | 414 |
| Income tax (expense) benefit on operating income (loss)                                | (60)           | (37)           | (145) | (141) |
| Net operating income (loss)                                                            | 114            | 75             | 280 | 273 |
| Net realized investment gains (losses), pre-tax                                        | 12             | (29)           | 2 | (23) |
| Income tax (expense) benefit on net realized investment gains (losses)                 | (3)            | 8              | 0 | 7 |
| Net realized investment gains (losses), after tax                                      | 9              | (21)           | 2 | (16) |
| Net Income (Loss)                                                                      | 123            | 54             | 282 | 257 |
| International [Member]                                                                 |           |           |   |   |
| **Operating Revenues**                                                                 |           |           |   |   |
| Net earned premiums                                                                    | 210            | 203            | 605 | 601 |
| Net investment income                                                                  | 13             | 13             | 38 | 40 |
| Other revenues                                                                         | 0              | 1              | 1 | 0 |
| Total operating revenues                                                               | 223            | 217            | 644 | 641 |
| **Claims, Benefits and Expenses**                                                      |           |           |   |   |
| Net incurred claims and benefits                                                       | 117            | 106            | 395 | 336 |
| Policyholders' dividends                                                               | 0              | 0              | 0 | 0 |
| Amortization of deferred acquisition costs                                             | 45             | 45             | 132 | 125 |
| Other insurance related expenses                                                       | 33             | 33             | 98 | 101 |
| Other expenses                                                                         | 1              | 9              | 17 | 9 |
| Total claims, benefits and expenses                                                    | 196            | 193            | 642 | 571 |
| Operating income (loss) before income tax                                              | 27             | 24             | 2 | 70 |
| Income tax (expense) benefit on operating income (loss)                                | (7)            | (15)           | (3) | (30) |
| Net operating income (loss)                                                            | 20             | 9              | (1) | 40 |
| Net realized investment gains (losses), pre-tax                                        | 6              | (1)            | 14 | 1 |
| Income tax (expense) benefit on net realized investment gains (losses)                 | (1)            | 1              | (3) | 0 |
| Net realized investment gains (losses), after tax                                      | 5              | 0              | 11 | 1 |
| Net Income (Loss)                                                                      | 25             | 9              | 10 | 41 |
| Life and Group Non-Core [Member]                                                       |           |           |   |   |
| **Operating Revenues**                                                                 |           |           |   |   |
| Net earned premiums                                                                    | 134            | 137            | 401 | 412 |
| Net investment income                                                                  | 192            | 182            | 567 | 540 |
| Other revenues                                                                         | (4)            | (1)            | (1) | 8 |
| Total operating revenues                                                               | 322            | 318            | 967 | 960 |
| **Claims, Benefits and Expenses**                                                      |           |           |   |   |
| Net incurred claims and benefits                                                       | 313            | 361            | 976 | 1,045 |
| Policyholders' dividends                                                               | 0              | 0              | 0 | 0 |
| Amortization of deferred acquisition costs                                             | 0              | 6              | 0 | 19 |
| Other insurance related expenses                                                       | 37             | 35             | 101 | 104 |
| Other expenses                                                                         | 2              | 1              | 7 | 10 |
| Total claims, benefits and expenses                                                    | 352            | 403            | 1,084 | 1,178 |
| Operating income (loss) before income tax                                              | (30)           | (85)           | (117) | (218) |
| Income tax (expense) benefit on operating income (loss)                                | 36             | 55             | 117 | 147 |
| Net operating income (loss)                                                            | 6              | (30)           | 0 | (71) |
| Net realized investment gains (losses), pre-tax                                        | 17             | 2              | 12 | (2) |
| Income tax (expense) benefit on net realized investment gains (losses)                 | (6)            | 0              | (9) | 8 |
| Net realized investment gains (losses), after tax                                      | 11             | 2              | 3 | 6 |
| Net Income (Loss)                                                                      | 17             | (28)           | 3 | (65) |
| Corporate and Other Non-Core [Member]                                                  |           |           |   |   |
| **Operating Revenues**                                                                 |           |           |   |   |
| Net earned premiums                                                                    | 0              | 0              | 0 | 0 |
| Net investment income                                                                  | 4              | 1              | 11 | 12 |
| Other revenues                                                                         | 0              | 4              | 3 | 9 |
| Total operating revenues                                                               | 4              | 5              | 14 | 21 |
| **Claims, Benefits and Expenses**                                                      |           |           |   |   |
| Net incurred claims and benefits                                                       | (11)           | (3)            | 109 | 78 |
| Policyholders' dividends                                                               | 0              | 0              | 0 | 0 |
| Amortization of deferred acquisition costs                                             | 0              | 0              | 0 | 0 |
| Other insurance related expenses                                                       | (3)            | 0              | (3) | (1) |
| Other expenses                                                                         | 57             | 47             | 158 | 140 |
| Total claims, benefits and expenses                                                    | 43             | 44             | 264 | 217 |
| Operating income (loss) before income tax                                              | (39)           | (39)           | (250) | (196) |
| Income tax (expense) benefit on operating income (loss)                                | 15             | 16             | 88 | 70 |
| Net operating income (loss)                                                            | (24)           | (23)           | (162) | (126) |
| Net realized investment gains (losses), pre-tax                                        | 2              | 1              | (4) | 3 |
| Income tax (expense) benefit on net realized investment gains (losses)                 | (1)            | 0              | 2 | (1) |
| Net realized investment gains (losses), after tax                                      | 1              | 1              | (2) | 2 |
| Net Income (Loss)                                                                      | (23)           | (22)           | (164) | (124) |
| Eliminations [Member]                                                                  |           |           |   |   |
| **Operating Revenues**                                                                 |           |           |   |   |
| Net earned premiums                                                                    | 0              | 0              | (1) | (1) |
| Net investment income                                                                  | 0              | 0              | 0 | 0 |
| Other revenues                                                                         | 0              | (2)            | 0 | (3) |
| Total operating revenues                                                               | 0              | (2)            | (1) | (4) |
| **Claims, Benefits and Expenses**                                                      |           |           |   |   |
| Net incurred claims and benefits                                                       | 0              | 0              | 0 | 0 |
| Policyholders' dividends                                                               | 0              | 0              | 0 | 0 |
| Amortization of deferred acquisition costs                                             | 0              | 0              | 0 | 0 |
| Other insurance related expenses                                                       | 0              | 0              | (1) | (1) |
| Other expenses                                                                         | 0              | (2)            | 0 | (3) |
| Total claims, benefits and expenses                                                    | 0              | (2)            | (1) | (4) |
| Operating income (loss) before income tax                                              | 0              | 0              | 0 | 0 |
| Income tax (expense) benefit on operating income (loss)                                | 0              | 0              | 0 | 0 |
| Net operating income (loss)                                                            | 0              | 0              | 0 | 0 |
| Net realized investment gains (losses), pre-tax                                        | 0              | 0              | 0 | 0 |
| Income tax (expense) benefit on net realized investment gains (losses)                 | 0              | 0              | 0 | 0 |
| Net realized investment gains (losses), after tax                                      | 0              | 0              | 0 | 0 |
| Net Income (Loss)                                                                      | $ 0            | $ 0            | $ 0 | $ 0 |

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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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Income Tax Expense (Benefit) on Net Realized Investment Gains Losses
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Income Tax Expense (Benefit) on Operating Income (Loss)
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| - Definition
Investment income derived from investments in debt and equity securities consisting of interest income earned from investments in debt securities and on cash and cash equivalents, dividend income from investments in equity securities and income or expense derived from the amortization of investment related discounts or premiums, respectively.  It also includes realized gains (losses) on trading securities.
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Net Operating Income (Loss) Attributable to Parent
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Net realized investment gains (losses)
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Operating Income (Loss) before Income Tax
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Operating Revenues
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| - Definition
Other Insurance Related Expenses
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| - Definition
This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.
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| - Definition
The total amount of expense recognized during the period for future policy benefits, claims and claims adjustment costs, and for selling, general and administrative costs.
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| - Definition
Amount of expense related to deferred policy acquisition costs.
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| - Definition
The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.
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| - Definition
This element represents a sum total of expenses not separately reflected on the income statement for the period.
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| - Definition
Reflects the sum of all other revenue and income recognized by the entity in the period not otherwise specified in the income statement.
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| - Definition
Amount, after effects of policies assumed or ceded, of expense related to the provision for policy benefits and costs incurred.
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| - Definition
Amount of expense for dividends to policyholders.
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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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