| **Income Taxes (Narrative) (Details) - USD ($)**                                   | 12 Months Ended |              |
|------------------------------------------------------------------------------------|-----------------|--------------|
||
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]**   |            |         |   |   |
| Income tax benefit for difference in tax rate                                      | $ 0             | $ 50,000,000 | $ 0 |   |
| Unrecognized Tax Benefits                                                          | 34,000,000      | 34,000,000   | 0 | $ 0 |
| Reduction in net deferred tax liability due to change of corporate income tax rate |            |         | 495,000,000 |   |
| Income taxes paid, net                                                             | 94,000,000      | 0            | 18,000,000 |   |
| Net deferred tax assets, valuation allowance                                       | 41,000,000      | 0            |   |   |
| Accumulated Other Comprehensive Income                                             |            |         |   |   |
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]**   |            |         |   |   |
| Reduction in net deferred tax liability due to change of corporate income tax rate |            |         | $ 492,000,000 |   |
| Cincinnati Global                                                                  |            |         |   |   |
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]**   |            |         |   |   |
| Net deferred tax assets                                                            | 41,000,000      |         |   |   |
| Net deferred tax assets, valuation allowance                                       | $ 41,000,000    | $ 0          |   |   |

| X                                                                                                                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Effective Income Tax Rate Reconciliation, Tax Accounting Method Changes, Amount
+ References
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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, without jurisdictional netting.
+ References
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| - Definition
Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income, net of any cash received during the current period as refunds for the overpayment of taxes.
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| - 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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| - Definition
Amount of reasonable estimate for income tax benefit for which accounting for tax effect for remeasurement of deferred tax liability from change in tax rate is incomplete pursuant to Tax Cuts and Jobs Act.
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| - Definition
Amount of unrecognized tax benefits.
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