| **Employee Retirement Benefits (Fair Value Hierarchy Of Assets Measured At Fair Value On A Recurring Basis) (Details) (USD $)In Millions, unless otherwise specified** | Dec. 31, 2014                                                                                                                                                                                                                                                                                                                          | Dec. 31, 2013                                                                                                                                                                                                                                                                                                                          |
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| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, debt securities                                                                                                                         | $ 9,460us-gaap_AvailableForSaleSecuritiesDebtSecurities                                                                                                                                                                                                                                                                                | $ 9,121us-gaap_AvailableForSaleSecuritiesDebtSecurities                                                                                                                                                                                                                                                                                |
| Available for sale securities, equity securities                                                                                                                       | 4,858us-gaap_AvailableForSaleSecuritiesEquitySecurities                                                                                                                                                                                                                                                                                | 4,375us-gaap_AvailableForSaleSecuritiesEquitySecurities                                                                                                                                                                                                                                                                                |
| Fixed Maturities                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, debt securities                                                                                                                         | 52us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember                                                                                                                                                                                                  | 53us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember                                                                                                                                                                                                  |
| Fixed Maturities | States, Municipalities and Political Subdivisions                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, debt securities                                                                                                                         | 33us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember                                                                                      | 32us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember                                                                                      |
| Fixed Maturities | Corporate Fixed Maturities                                                                                                                          |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, debt securities                                                                                                                         | 19us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CorporateDebtSecuritiesMember                                                                                               | 21us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CorporateDebtSecuritiesMember                                                                                               |
| Equity Securities                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, equity securities                                                                                                                       | 277us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_EquitySecuritiesMember                                                                                                                                                                                             | 261us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_EquitySecuritiesMember                                                                                                                                                                                             |
| Equity Securities | Common Stock                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, equity securities                                                                                                                       | 225us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_EquitySecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CommonStockMember                                                                                                      | 208us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_EquitySecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CommonStockMember                                                                                                      |
| Level 1 | Fixed Maturities                                                                                                                                             |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, debt securities                                                                                                                         | 0us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel1Member                                                                                                              | 0us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel1Member                                                                                                              |
| Level 1 | Fixed Maturities | States, Municipalities and Political Subdivisions                                                                                         |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, debt securities                                                                                                                         | 0us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel1Member  | 0us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel1Member  |
| Level 1 | Fixed Maturities | Corporate Fixed Maturities                                                                                                                |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, debt securities                                                                                                                         | 0us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CorporateDebtSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel1Member           | 0us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CorporateDebtSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel1Member           |
| Level 1 | Equity Securities                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, equity securities                                                                                                                       | 225us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_EquitySecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel1Member                                                                                                        | 208us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_EquitySecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel1Member                                                                                                        |
| Level 1 | Equity Securities | Common Stock                                                                                                                             |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, equity securities                                                                                                                       | 225us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_EquitySecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CommonStockMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel1Member                 | 208us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_EquitySecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CommonStockMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel1Member                 |
| Level 2                                                                                                                                                                |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, equity securities                                                                                                                       |                                                                                                                                                                                                                                                                                                                                   | 53us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel2Member                                                                                                                                                                                              |
| Level 2 | Fixed Maturities                                                                                                                                             |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, debt securities                                                                                                                         | 52us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel2Member                                                                                                             | 53us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel2Member                                                                                                             |
| Level 2 | Fixed Maturities | States, Municipalities and Political Subdivisions                                                                                         |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, debt securities                                                                                                                         | 33us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel2Member | 32us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel2Member |
| Level 2 | Fixed Maturities | Corporate Fixed Maturities                                                                                                                |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, debt securities                                                                                                                         | 19us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CorporateDebtSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel2Member          | 21us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CorporateDebtSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel2Member          |
| Level 2 | Equity Securities                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, equity securities                                                                                                                       | 52us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_EquitySecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel2Member                                                                                                         |                                                                                                                                                                                                                                                                                                                                   |
| Level 2 | Equity Securities | Common Stock                                                                                                                             |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, equity securities                                                                                                                       | 0us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_EquitySecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CommonStockMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel2Member                   | 0us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_EquitySecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CommonStockMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel2Member                   |
| Level 3                                                                                                                                                                |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, equity securities                                                                                                                       |                                                                                                                                                                                                                                                                                                                                   | 0us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member                                                                                                                                                                                               |
| Level 3 | Fixed Maturities                                                                                                                                             |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, debt securities                                                                                                                         | 0us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member                                                                                                              | 0us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member                                                                                                              |
| Level 3 | Fixed Maturities | States, Municipalities and Political Subdivisions                                                                                         |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, debt securities                                                                                                                         | 0us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member  | 0us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member  |
| Level 3 | Fixed Maturities | Corporate Fixed Maturities                                                                                                                |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, debt securities                                                                                                                         | 0us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CorporateDebtSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member           | 0us-gaap_AvailableForSaleSecuritiesDebtSecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_DebtSecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CorporateDebtSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member           |
| Level 3 | Equity Securities                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, equity securities                                                                                                                       | 0us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_EquitySecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member                                                                                                          |                                                                                                                                                                                                                                                                                                                                   |
| Level 3 | Equity Securities | Common Stock                                                                                                                             |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| **Schedule of Pension and Other Postretirment Plan Assets by Fair Value**                                                                                              |                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                   |
| Available for sale securities, equity securities                                                                                                                       | $ 0us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_EquitySecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CommonStockMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member                 | $ 0us-gaap_AvailableForSaleSecuritiesEquitySecurities/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis= us-gaap_EquitySecuritiesMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CommonStockMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member                 |

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| - Definition
Amount of debt securities categorized neither as held-to-maturity nor trading.
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| - Definition
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