| **Investments (Analysis Of Cost Or Amortized Cost Gross Unrealized Gains And Losses And Fair Value For Investments) (Details) (USD $)In Millions, unless otherwise specified** | Dec. 31, 2014                                                                                                                                                                                                                           | Dec. 31, 2013                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Fixed Maturities                                                                                                                                                               |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| **Schedule of Available-for-sale Securities**                                                                                                                                  |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| Cost or amortized cost                                                                                                                                                         | $ 8,871us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember                                                                                                              | $ 8,638us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember                                                                                                               |
| Gross unrealized gains                                                                                                                                                         | 607cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember                                                                                                              | 558cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember                                                                                                               |
| Gross unrealized losses                                                                                                                                                        | 18cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember                                                                                                               | 75cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember                                                                                                                |
| Fair value                                                                                                                                                                     | 9,460us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember                                                                                                                             | 9,121us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember                                                                                                                              |
| Fixed Maturities | Corporate Securities                                                                                                                                        |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| **Schedule of Available-for-sale Securities**                                                                                                                                  |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| Cost or amortized cost                                                                                                                                                         | 5,117us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CorporateBondSecuritiesMember                        | 5,122us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CorporateBondSecuritiesMember                         |
| Gross unrealized gains                                                                                                                                                         | 420cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CorporateBondSecuritiesMember                      | 433cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CorporateBondSecuritiesMember                       |
| Gross unrealized losses                                                                                                                                                        | 11cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CorporateBondSecuritiesMember                       | 22cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CorporateBondSecuritiesMember                        |
| Fair value                                                                                                                                                                     | 5,526us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CorporateBondSecuritiesMember                                     | 5,533us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CorporateBondSecuritiesMember                                      |
| Fixed Maturities | States, Municipalities and Political Subdivisions                                                                                                           |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| **Schedule of Available-for-sale Securities**                                                                                                                                  |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| Cost or amortized cost                                                                                                                                                         | 3,267us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember               | 3,107us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember                |
| Gross unrealized gains                                                                                                                                                         | 178cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember             | 125cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember              |
| Gross unrealized losses                                                                                                                                                        | 2cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember               | 21cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember               |
| Fair value                                                                                                                                                                     | 3,443us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember                            | 3,211us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember                             |
| Fixed Maturities | Commercial Mortgage Backed Securities                                                                                                                       |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| **Schedule of Available-for-sale Securities**                                                                                                                                  |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| Cost or amortized cost                                                                                                                                                         | 250us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommercialMortgageBackedSecuritiesMember               | 148us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommercialMortgageBackedSecuritiesMember                |
| Gross unrealized gains                                                                                                                                                         | 9cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommercialMortgageBackedSecuritiesMember             | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommercialMortgageBackedSecuritiesMember              |
| Gross unrealized losses                                                                                                                                                        | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommercialMortgageBackedSecuritiesMember             | 5cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommercialMortgageBackedSecuritiesMember              |
| Fair value                                                                                                                                                                     | 259us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommercialMortgageBackedSecuritiesMember                            | 143us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommercialMortgageBackedSecuritiesMember                             |
| Fixed Maturities | Government-Sponsored Enterprises                                                                                                                            |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| **Schedule of Available-for-sale Securities**                                                                                                                                  |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| Cost or amortized cost                                                                                                                                                         | 213us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember   | 227us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember    |
| Gross unrealized gains                                                                                                                                                         | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember  |
| Gross unrealized losses                                                                                                                                                        | 5cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 27cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember |
| Fair value                                                                                                                                                                     | 208us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember                | 200us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember                 |
| Fixed Maturities | Foreign Government                                                                                                                                          |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| **Schedule of Available-for-sale Securities**                                                                                                                                  |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| Cost or amortized cost                                                                                                                                                         | 10us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= cinf_ForeignGovernmentMember                                    | 10us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= cinf_ForeignGovernmentMember                                     |
| Gross unrealized gains                                                                                                                                                         | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= cinf_ForeignGovernmentMember                                 | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= cinf_ForeignGovernmentMember                                  |
| Gross unrealized losses                                                                                                                                                        | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= cinf_ForeignGovernmentMember                                 | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= cinf_ForeignGovernmentMember                                  |
| Fair value                                                                                                                                                                     | 10us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= cinf_ForeignGovernmentMember                                                 | 10us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= cinf_ForeignGovernmentMember                                                  |
| Fixed Maturities | Convertibles and Bonds with Warrants Attached                                                                                                               |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| **Schedule of Available-for-sale Securities**                                                                                                                                  |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| Cost or amortized cost                                                                                                                                                         | 7us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_ConvertiblesAndBondsWithWarrantsAttachedMember           | 17us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_ConvertiblesAndBondsWithWarrantsAttachedMember           |
| Gross unrealized gains                                                                                                                                                         | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_ConvertiblesAndBondsWithWarrantsAttachedMember       | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_ConvertiblesAndBondsWithWarrantsAttachedMember        |
| Gross unrealized losses                                                                                                                                                        | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_ConvertiblesAndBondsWithWarrantsAttachedMember       | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_ConvertiblesAndBondsWithWarrantsAttachedMember        |
| Fair value                                                                                                                                                                     | 7us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_ConvertiblesAndBondsWithWarrantsAttachedMember                        | 17us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_ConvertiblesAndBondsWithWarrantsAttachedMember                        |
| Fixed Maturities | United States Government                                                                                                                                    |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| **Schedule of Available-for-sale Securities**                                                                                                                                  |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| Cost or amortized cost                                                                                                                                                         | 7us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentAgenciesDebtSecuritiesMember                 | 7us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentAgenciesDebtSecuritiesMember                  |
| Gross unrealized gains                                                                                                                                                         | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentAgenciesDebtSecuritiesMember             | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentAgenciesDebtSecuritiesMember              |
| Gross unrealized losses                                                                                                                                                        | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentAgenciesDebtSecuritiesMember             | 0cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentAgenciesDebtSecuritiesMember              |
| Fair value                                                                                                                                                                     | 7us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentAgenciesDebtSecuritiesMember                              | 7us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_DebtSecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_USGovernmentAgenciesDebtSecuritiesMember                               |
| Equity Securities                                                                                                                                                              |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| **Schedule of Available-for-sale Securities**                                                                                                                                  |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| Cost or amortized cost                                                                                                                                                         | 2,728us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember                                                                                                              | 2,523us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember                                                                                                               |
| Gross unrealized gains                                                                                                                                                         | 2,134cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember                                                                                                          | 1,856cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember                                                                                                           |
| Gross unrealized losses                                                                                                                                                        | 4cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember                                                                                                              | 4cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember                                                                                                               |
| Fair value                                                                                                                                                                     | 4,858us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember                                                                                                                           | 4,375us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember                                                                                                                            |
| Equity Securities | Common Equities                                                                                                                                            |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| **Schedule of Available-for-sale Securities**                                                                                                                                  |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| Cost or amortized cost                                                                                                                                                         | 2,583us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommonStockMember                                  | 2,396us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommonStockMember                                   |
| Gross unrealized gains                                                                                                                                                         | 2,099cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommonStockMember                              | 1,818cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommonStockMember                               |
| Gross unrealized losses                                                                                                                                                        | 3cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommonStockMember                                  | 1cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommonStockMember                                   |
| Fair value                                                                                                                                                                     | 4,679us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommonStockMember                                               | 4,213us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_CommonStockMember                                                |
| Equity Securities | Nonredeemable Preferred Equities                                                                                                                           |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| **Schedule of Available-for-sale Securities**                                                                                                                                  |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| Cost or amortized cost                                                                                                                                                         | 145us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_PreferredStockMember                                 | 127us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_PreferredStockMember                                  |
| Gross unrealized gains                                                                                                                                                         | 35cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_PreferredStockMember                              | 38cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_PreferredStockMember                               |
| Gross unrealized losses                                                                                                                                                        | 1cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_PreferredStockMember                               | 3cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_PreferredStockMember                                |
| Fair value                                                                                                                                                                     | 179us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_PreferredStockMember                                              | 162us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= us-gaap_EquitySecuritiesMember/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_PreferredStockMember                                               |
| Fixed Maturities And Equity Securities                                                                                                                                         |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| **Schedule of Available-for-sale Securities**                                                                                                                                  |                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                     |
| Cost or amortized cost                                                                                                                                                         | 11,599us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= cinf_FixedMaturitiesAndEquitySecuritiesMember                                                                                              | 11,161us-gaap_AvailableForSaleSecuritiesAmortizedCost/ invest_InvestmentSecuritiesClassAxis= cinf_FixedMaturitiesAndEquitySecuritiesMember                                                                                               |
| Gross unrealized gains                                                                                                                                                         | 2,741cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= cinf_FixedMaturitiesAndEquitySecuritiesMember                                                                                           | 2,414cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1/ invest_InvestmentSecuritiesClassAxis= cinf_FixedMaturitiesAndEquitySecuritiesMember                                                                                            |
| Gross unrealized losses                                                                                                                                                        | 22cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= cinf_FixedMaturitiesAndEquitySecuritiesMember                                                                                              | 79cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2/ invest_InvestmentSecuritiesClassAxis= cinf_FixedMaturitiesAndEquitySecuritiesMember                                                                                               |
| Fair value                                                                                                                                                                     | $ 14,318us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= cinf_FixedMaturitiesAndEquitySecuritiesMember                                                                                                         | $ 13,496us-gaap_AvailableForSaleSecurities/ invest_InvestmentSecuritiesClassAxis= cinf_FixedMaturitiesAndEquitySecuritiesMember                                                                                                          |

| X                                                                                                                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.
+ References
No definition available.
+ Details**Name:**cinf_AvailableforsaleSecuritiesGrossUnrealizedGain1**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.
+ References
No definition available.
+ Details**Name:**cinf_AvailableforsaleSecuritiesGrossUnrealizedLoss2**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.
+ References
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| - Definition
This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.
+ References
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