| **Condensed Financial Statements Of Parent Company Condensed Balance Sheets (Parenthetical) (Details) - USD ($) $ in Millions** | Dec. 31, 2019 | Dec. 31, 2018 |
|---------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Condensed Financial Statements, Captions**                                                                                    |          |          |
| Fixed maturities, amortized cost                                                                                                | $ 11,108      | $ 10,643      |
| Equity securities, cost                                                                                                         | 3,581         | 3,368         |
| Land, building and equipment, accumulated depreciation                                                                          | 276           | 265           |
| Cincinnati Financial Corporation                                                                                                |          |          |
| **Condensed Financial Statements, Captions**                                                                                    |          |          |
| Fixed maturities, amortized cost                                                                                                | 49            | 35            |
| Equity securities, cost                                                                                                         | 1,427         | 1,282         |
| Land, building and equipment, accumulated depreciation                                                                          | $ 129         | $ 121         |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the cost of equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments made for accretion, amortization, other-than-temporary impairments, and hedging, if any.
+ References
No definition available.
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| 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.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
+ References
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| X                                                                                                                                            |
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