| **Income Taxes (Significant components of the Company's deferred tax assets and liabilities) (Details) - USD ($) $ in Millions** | Dec. 31, 2021 | Dec. 31, 2020 |
|----------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Deferred Tax Assets:**                                                                                                         |          |          |
| Property and casualty claim and claim adjustment expense reserves                                                                | $ 173         | $ 157         |
| Unearned premium reserves                                                                                                        | 193           | 174           |
| Deferred Revenue                                                                                                                 | 64            | 62            |
| Employee benefits                                                                                                                | 46            | 122           |
| Deferred retroactive reinsurance benefit                                                                                         | 90            | 83            |
| Other assets                                                                                                                     | 88            | 92            |
| Gross deferred tax assets                                                                                                        | 654           | 690           |
| **Deferred Tax Liabilities:**                                                                                                    |          |          |
| Investment valuation differences                                                                                                 | 93            | 28            |
| Deferred acquisition costs                                                                                                       | 99            | 93            |
| Net unrealized gains                                                                                                             | 272           | 453           |
| Software and hardware                                                                                                            | 27            | 31            |
| Other liabilities                                                                                                                | 21            | 19            |
| Gross deferred tax liabilities                                                                                                   | 512           | 624           |
| Net deferred tax asset                                                                                                           | $ 142         | $ 66          |

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| - Definition
Amount of deferred tax liability attributable to taxable temporary differences.
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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from deferred income.
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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.
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Amount, after allocation of valuation allowances and deferred tax liability, of deferred tax asset attributable to deductible differences and carryforwards, without jurisdictional netting.
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Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences, classified as other.
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Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences from employee benefits, classified as other.
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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 classified as other.
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Amount of deferred tax liability attributable to taxable temporary differences from unrealized gains in other comprehensive income.
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