| **Income Taxes (Narrative) (Details) - USD ($) $ in Millions** | 3 Months Ended | 9 Months Ended |        |
|----------------------------------------------------------------|----------------|----------------|--------|
||
| **Income Tax Contingency**                                     |           |           |   |   |   |
| Tax at statutory rate, percentage                              | 21.00%         | 21.00%         | 21.00% | 21.00% |   |
| Deferred tax assets valuation allowance                        | $ 0            |           | $ 0    |   | $ 0 |
| Cincinnati Global                                              |           |           |   |   |   |
| **Income Tax Contingency**                                     |           |           |   |   |   |
| Decrease in deferred tax assets                                | 7              |           | 4      |   |   |
| Decrease in deferred tax valuation allowance                   | 7              |           | 4      |   |   |
| Net deferred tax assets                                        | 49             |           | 49     |   |   |
| Deferred tax assets valuation allowance                        | 49             |           | 49     |   |   |
| Cincinnati Global | United States                              |           |           |   |   |   |
| **Income Tax Contingency**                                     |           |           |   |   |   |
| Operating loss carryforwards                                   | 6              |           | 6      |   | 8 |
| Cincinnati Global | United Kingdom                             |           |           |   |   |   |
| **Income Tax Contingency**                                     |           |           |   |   |   |
| Operating loss carryforwards                                   | $ 123          |           | $ 123  |   | $ 130 |

| X                                                                                                                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Increase (Decrease) of deferred tax assets
+ References
No definition available.
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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.
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of domestic federal statutory tax rate applicable to pretax income (loss).
+ References
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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 operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset.
+ References
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