| **Income Taxes (Significant components of the Company's deferred tax assets and liabilities) (Details) - USD ($) $ in Millions** | Dec. 31, 2015 | Dec. 31, 2014 |
|----------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Deferred Tax Assets:**                                                                                                         |          |          |
| Property and casualty claim and claim adjustment expense reserves                                                                | $ 178         | $ 265         |
| Unearned premium reserves                                                                                                        | 230           | 187           |
| Receivables                                                                                                                      | 29            | 35            |
| Employee benefits                                                                                                                | 281           | 289           |
| Life settlement contracts                                                                                                        | 48            | 46            |
| Deferred retroactive reinsurance benefit                                                                                         | 84            | 61            |
| Investment valuation differences                                                                                                 | 29            | 0             |
| Other assets                                                                                                                     | 142           | 138           |
| Gross deferred tax assets                                                                                                        | 1,021         | 1,021         |
| **Deferred Tax Liabilities:**                                                                                                    |          |          |
| Investment valuation differences                                                                                                 | 0             | 50            |
| Deferred acquisition costs                                                                                                       | 117           | 226           |
| Net unrealized gains                                                                                                             | 202           | 489           |
| Other liabilities                                                                                                                | 64            | 65            |
| Deferred Tax Liabilities, Gross                                                                                                  | 383           | 830           |
| Net deferred tax asset (liability)                                                                                               | $ 638         | $ 191         |

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Deferred Tax Assets Deferred Retroactive Reinsurance Benefit
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Deferred Tax Assets Life Settlement Contracts
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| - Definition
Amount of deferred tax liability attributable to taxable temporary differences.
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| - Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.
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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from investments (excludes investments in subsidiaries and equity method investments).
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| - Definition
Amount, after allocation of valuation allowances and deferred tax liability, of deferred tax asset attributable to deductible differences and carryforwards, before jurisdictional netting.
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| - Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences not separately disclosed.
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| - Definition
The tax effect as of the balance sheet date of the amount of the estimated future tax deductions arising from employee benefit costs not otherwise specified in the taxonomy, which can only be deducted for tax purposes when actual costs are incurred, and which can only be realized if sufficient tax-basis income is generated in future periods to enable the deduction to be taken.
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| - Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from the allowance for doubtful accounts.
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| - Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from loss reserves other than estimated credit losses.
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| - Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from the unearned premiums reserve.
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| - Definition
The amount as of the balance sheet date of the estimated future tax effects attributable to policy acquisition costs being expensed for tax purposes but capitalized in conformity with generally accepted accounting principles, which will reverse in future periods when amortization of such capitalized costs cannot be deducted for tax purposes.
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Amount of deferred tax liability attributable to taxable temporary differences from investments (excludes investments in subsidiaries and equity method investments).
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| - Definition
Amount of deferred tax liability attributable to taxable temporary differences not separately disclosed.
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of deferred tax liability attributable to taxable temporary differences from unrealized gains in other comprehensive income.
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