| **Supplementary Information Concerning Property Casualty Insurance Operations (Details) (USD $)In Millions, unless otherwise specified** | 12 Months Ended                                                                                                                                                                                                                       |
|------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]**                                                  |                                                                                                                                                                                                                                  |   |   |
| Deferred policy acquisition costs                                                                                                        | $ 379us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersDeferredPolicyAcquisitionCosts                                                                                                                            | $ 366us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersDeferredPolicyAcquisitionCosts | $ 337us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersDeferredPolicyAcquisitionCosts |
| Reserves for unpaid claims and claim adjustment expenses                                                                                 | 4,438us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersReservesForUnpaidClaimsAndClaimsAdjustmentExpense                                                                                                         | 4,241us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersReservesForUnpaidClaimsAndClaimsAdjustmentExpense | 4,169us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersReservesForUnpaidClaimsAndClaimsAdjustmentExpense |
| Unearned premiums                                                                                                                        | 2,081us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersUnearnedPremiums                                                                                                                                          | 1,970us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersUnearnedPremiums | 1,790us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersUnearnedPremiums |
| Earned premiums                                                                                                                          | 4,045us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersEarnedPremiums                                                                                                                                            | 3,713us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersEarnedPremiums | 3,344us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersEarnedPremiums |
| Investment income                                                                                                                        | 358us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersNetInvestmentIncome                                                                                                                                         | 348us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersNetInvestmentIncome | 351us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersNetInvestmentIncome |
| Loss and loss expenses incurred related to current accident year                                                                         | 2,725us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense                                                                                                               | 2,448us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense | 2,533us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense |
| Prior year claims and claims adjustment expense                                                                                          | (98)us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense                                                                                                                  | (147)us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense | (396)us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense |
| Amortization of deferred policy acquisition cost                                                                                         | 770us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersAmortizationOfDeferredPolicyAcquisitionCosts                                                                                                                | 727us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersAmortizationOfDeferredPolicyAcquisitionCosts | 661us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersAmortizationOfDeferredPolicyAcquisitionCosts |
| Paid loss and loss expenses                                                                                                              | 2,413us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPaidClaimsAndClaimsAdjustmentExpense                                                                                                                      | 2,172us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPaidClaimsAndClaimsAdjustmentExpense | 2,229us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPaidClaimsAndClaimsAdjustmentExpense |
| Net written premiums                                                                                                                     | 4,143us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPremiumsWritten                                                                                                                                           | 3,893us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPremiumsWritten | 3,482us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPremiumsWritten |
| Commercial Insurance                                                                                                                     |                                                                                                                                                                                                                                  |   |   |
| **Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]**                                                  |                                                                                                                                                                                                                                  |   |   |
| Deferred policy acquisition costs                                                                                                        | 257us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember                      | 251us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 235us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Reserves for unpaid claims and claim adjustment expenses                                                                                 | 3,797us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersReservesForUnpaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 3,667us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersReservesForUnpaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 3,645us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersReservesForUnpaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Unearned premiums                                                                                                                        | 1,441us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersUnearnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember                                  | 1,370us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersUnearnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 1,246us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersUnearnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Earned premiums                                                                                                                          | 2,856us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersEarnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember                                    | 2,636us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersEarnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 2,383us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersEarnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Investment income                                                                                                                        | 0us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersNetInvestmentIncome/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember                                   | 0us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersNetInvestmentIncome/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 0us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersNetInvestmentIncome/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Loss and loss expenses incurred related to current accident year                                                                         | 1,869us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember       | 1,691us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 1,712us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Prior year claims and claims adjustment expense                                                                                          | (57)us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember          | (95)us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | (292)us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Amortization of deferred policy acquisition cost                                                                                         | 537us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersAmortizationOfDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember        | 514us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersAmortizationOfDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 461us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersAmortizationOfDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Paid loss and loss expenses                                                                                                              | 1,666us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember              | 1,498us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 1,546us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Net written premiums                                                                                                                     | 2,922us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPremiumsWritten/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember                                   | 2,760us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPremiumsWritten/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 2,459us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPremiumsWritten/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Personal Insurance                                                                                                                       |                                                                                                                                                                                                                                  |   |   |
| **Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]**                                                  |                                                                                                                                                                                                                                  |   |   |
| Deferred policy acquisition costs                                                                                                        | 108us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember                        | 104us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 93us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Reserves for unpaid claims and claim adjustment expenses                                                                                 | 439us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersReservesForUnpaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember     | 417us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersReservesForUnpaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 398us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersReservesForUnpaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Unearned premiums                                                                                                                        | 562us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersUnearnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember                                      | 534us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersUnearnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 490us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersUnearnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Earned premiums                                                                                                                          | 1,041us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersEarnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember                                      | 961us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersEarnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 868us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersEarnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Investment income                                                                                                                        | 0us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersNetInvestmentIncome/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember                                     | 0us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersNetInvestmentIncome/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 0us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersNetInvestmentIncome/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Loss and loss expenses incurred related to current accident year                                                                         | 752us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember           | 678us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 751us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Prior year claims and claims adjustment expense                                                                                          | (12)us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember            | (39)us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | (99)us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Amortization of deferred policy acquisition cost                                                                                         | 209us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersAmortizationOfDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember          | 192us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersAmortizationOfDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 183us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersAmortizationOfDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Paid loss and loss expenses                                                                                                              | 717us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember                  | 639us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 659us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Net written premiums                                                                                                                     | 1,068us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPremiumsWritten/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember                                     | 1,005us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPremiumsWritten/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 918us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPremiumsWritten/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Excess And Surplus Lines Insurance                                                                                                       |                                                                                                                                                                                                                                  |   |   |
| **Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]**                                                  |                                                                                                                                                                                                                                  |   |   |
| Deferred policy acquisition costs                                                                                                        | 14us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember                                             | 11us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember | 9us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember |
| Reserves for unpaid claims and claim adjustment expenses                                                                                 | 202us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersReservesForUnpaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember                         | 157us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersReservesForUnpaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember | 126us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersReservesForUnpaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember |
| Unearned premiums                                                                                                                        | 78us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersUnearnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember                                                           | 66us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersUnearnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember | 54us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersUnearnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember |
| Earned premiums                                                                                                                          | 148us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersEarnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember                                                            | 116us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersEarnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember | 93us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersEarnedPremiums/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember |
| Investment income                                                                                                                        | 0us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersNetInvestmentIncome/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember                                                         | 0us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersNetInvestmentIncome/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember | 0us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersNetInvestmentIncome/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember |
| Loss and loss expenses incurred related to current accident year                                                                         | 104us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember                               | 79us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember | 70us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember |
| Prior year claims and claims adjustment expense                                                                                          | (29)us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember                                | (13)us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember | (5)us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember |
| Amortization of deferred policy acquisition cost                                                                                         | 24us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersAmortizationOfDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember                               | 21us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersAmortizationOfDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember | 17us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersAmortizationOfDeferredPolicyAcquisitionCosts/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember |
| Paid loss and loss expenses                                                                                                              | 30us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember                                       | 35us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember | 24us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPaidClaimsAndClaimsAdjustmentExpense/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember |
| Net written premiums                                                                                                                     | $ 153us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPremiumsWritten/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember                                                         | $ 128us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPremiumsWritten/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember | $ 105us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPremiumsWritten/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessAndSurplusLinesInsuranceMember |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of amortization expense on deferred policy acquisition cost.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of expense for claims incurred in the current reporting period and related claims settlement costs.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-18) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e575016-122915Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 18 -Article 12
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of deferred policy acquisition cost related to property-casualty insurance policy written.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-18) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e575016-122915Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 18 -Article 12
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of property-casualty insurance premium revenue earned on insurance policies.
+ References
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| X                                                                                                                                                                                                            |
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of net investment income earned by property-casualty insurance underwriter.
+ References
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| - Definition
Payments of claims and claims adjustment expenses during the period of a property-casualty insurance entity.
+ References
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| - Definition
Amount of actual premium written by property-casualty insurance underwriter.
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| - Definition
Amount of expense for claims incurred in prior reporting periods and related claims settlement costs.
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| - Definition
The amount of reserve, policy claim payable and loss expense incurred by property-casualty insurance underwriter.
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| - Definition
Amount of property-casualty insurance premium revenue not yet earned on insurance policies.
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