| **Claim and Claim Adjustment Expense Reserves (Commercial - Detail of Develpment Recorded) (Details) - Commercial - USD ($) $ in Millions** | 3 Months Ended | 6 Months Ended |
|---------------------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|
||
| **Liability for Claims and Claims Adjustment Expense [Line Items]**                                                                         |           |           |   |   |
| Total pretax (favorable) unfavorable development                                                                                            | $ (13)         | $ (34)         | $ (22) | $ (77) |
| Commercial Auto                                                                                                                             |           |           |   |   |
| **Liability for Claims and Claims Adjustment Expense [Line Items]**                                                                         |           |           |   |   |
| Total pretax (favorable) unfavorable development                                                                                            | 0              | 1              | (1) | (25) |
| General Liability                                                                                                                           |           |           |   |   |
| **Liability for Claims and Claims Adjustment Expense [Line Items]**                                                                         |           |           |   |   |
| Total pretax (favorable) unfavorable development                                                                                            | 26             | 1              | 18 | (17) |
| Workers' Compensation                                                                                                                       |           |           |   |   |
| **Liability for Claims and Claims Adjustment Expense [Line Items]**                                                                         |           |           |   |   |
| Total pretax (favorable) unfavorable development                                                                                            | (6)            | (47)           | (12) | (47) |
| Property and Other                                                                                                                          |           |           |   |   |
| **Liability for Claims and Claims Adjustment Expense [Line Items]**                                                                         |           |           |   |   |
| Total pretax (favorable) unfavorable development                                                                                            | $ (33)         | $ 11           | $ (27) | $ 12 |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after effects of reinsurance, of increase (decrease) in the liability for unpaid claims and claims adjustment expense.
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437
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