| **Property Casualty Loss And Loss Expenses (Average Annual Payout) (Details)**  | Dec. 31, 2016 |
|---------------------------------------------------------------------------------|---------------|
| Commercial Insurance | Commercial Auto Line                                     |          |
| **Short-duration Insurance Contracts, Historical Claims Duration [Line Items]** |          |
| 1                                                                               | 44.40%        |
| 2                                                                               | 18.40%        |
| 3                                                                               | 13.90%        |
| 4                                                                               | 12.20%        |
| 5                                                                               | 6.90%         |
| Commercial Insurance | Workers' Compensation Line                               |          |
| **Short-duration Insurance Contracts, Historical Claims Duration [Line Items]** |          |
| 1                                                                               | 25.70%        |
| 2                                                                               | 26.90%        |
| 3                                                                               | 12.70%        |
| 4                                                                               | 7.10%         |
| 5                                                                               | 4.40%         |
| 6                                                                               | 2.40%         |
| 7                                                                               | 1.60%         |
| 8                                                                               | 1.40%         |
| 9                                                                               | 1.20%         |
| 10                                                                              | 0.50%         |
| Commercial Insurance | Commercial Casualty Line                                 |          |
| **Short-duration Insurance Contracts, Historical Claims Duration [Line Items]** |          |
| 1                                                                               | 8.00%         |
| 2                                                                               | 15.40%        |
| 3                                                                               | 17.70%        |
| 4                                                                               | 16.50%        |
| 5                                                                               | 13.80%        |
| 6                                                                               | 8.30%         |
| 7                                                                               | 4.70%         |
| 8                                                                               | 4.00%         |
| 9                                                                               | 1.50%         |
| 10                                                                              | 2.90%         |
| Commercial Insurance | Commercial Auto Line                                     |          |
| **Short-duration Insurance Contracts, Historical Claims Duration [Line Items]** |          |
| 1                                                                               | 65.00%        |
| 2                                                                               | 26.80%        |
| 3                                                                               | 4.60%         |
| 4                                                                               | 1.20%         |
| 5                                                                               | 0.90%         |
| Personal Insurance | Home Owner Line                                            |          |
| **Short-duration Insurance Contracts, Historical Claims Duration [Line Items]** |          |
| 1                                                                               | 73.80%        |
| 2                                                                               | 19.70%        |
| 3                                                                               | 2.60%         |
| 4                                                                               | 1.00%         |
| 5                                                                               | 0.30%         |
| Personal Insurance | Personal Auto                                              |          |
| **Short-duration Insurance Contracts, Historical Claims Duration [Line Items]** |          |
| 1                                                                               | 64.00%        |
| 2                                                                               | 17.90%        |
| 3                                                                               | 9.60%         |
| 4                                                                               | 4.80%         |
| 5                                                                               | 2.00%         |
| Excess and Surplus Lines Insurance                                              |          |
| **Short-duration Insurance Contracts, Historical Claims Duration [Line Items]** |          |
| 1                                                                               | 15.90%        |
| 2                                                                               | 13.50%        |
| 3                                                                               | 17.40%        |
| 4                                                                               | 13.50%        |
| 5                                                                               | 9.90%         |
| 6                                                                               | 7.40%         |

| 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.
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No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of average annual payout, after reinsurance, in the eighth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of average annual payout, after reinsurance, in the fifth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4G -URI http://asc.fasb.org/extlink&oid=65670685&loc=SL65671329-158438
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of average annual payout, after reinsurance, in the fourth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4G -URI http://asc.fasb.org/extlink&oid=65670685&loc=SL65671329-158438
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of average annual payout, after reinsurance, in the ninth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4G -URI http://asc.fasb.org/extlink&oid=65670685&loc=SL65671329-158438
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of average annual payout, after reinsurance, in the first year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of average annual payout, after reinsurance, in the seventh year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.
+ References
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| - Definition
Percentage of average annual payout, after reinsurance, in the sixth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
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| - Definition
Percentage of average annual payout, after reinsurance, in the tenth year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.
+ References
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| - Definition
Percentage of average annual payout, after reinsurance, in the third year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.
+ References
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| - Definition
Percentage of average annual payout, after reinsurance, in the second year after a claim is incurred, beginning with the earliest accident year disclosed for short-duration insurance contracts.
+ References
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