| **Segment Information (Detail) (USD $)In Millions, unless otherwise specified** | 3 Months Ended                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                               |
|---------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Earned premiums                                                                 | $ 1,094us-gaap_PremiumsEarnedNet                                                                                                                                                                                                                                                               | $ 1,027us-gaap_PremiumsEarnedNet                                                                                                                                                                                                                                                              |   |
| Fee revenues                                                                    | 3us-gaap_FeesAndCommissions                                                                                                                                                                                                                                                                    | 3us-gaap_FeesAndCommissions                                                                                                                                                                                                                                                                   |   |
| Investment income, net of expenses                                              | 139us-gaap_NetInvestmentIncome                                                                                                                                                                                                                                                                 | 135us-gaap_NetInvestmentIncome                                                                                                                                                                                                                                                                |   |
| Realized investment gains, net                                                  | 47us-gaap_RealizedInvestmentGainsLosses                                                                                                                                                                                                                                                        | 22us-gaap_RealizedInvestmentGainsLosses                                                                                                                                                                                                                                                       |   |
| Other                                                                           | 2us-gaap_OtherIncome                                                                                                                                                                                                                                                                           | 2us-gaap_OtherIncome                                                                                                                                                                                                                                                                          |   |
| Revenues                                                                        | 1,285us-gaap_Revenues                                                                                                                                                                                                                                                                          | 1,189us-gaap_Revenues                                                                                                                                                                                                                                                                         |   |
| Income (loss) before income taxes                                               | 174us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments                                                                                                                                                                         | 119us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments                                                                                                                                                                        |   |
| Identifiable assets                                                             | 18,897us-gaap_Assets                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          | 18,753us-gaap_Assets |
| Consolidated Property and Casualty Insurance Entity                             |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Identifiable assets                                                             | 2,711us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_ConsolidatedPropertyAndCasualtyInsuranceEntityMember                                                                                                                                                                       |                                                                                                                                                                                                                                                                                          | 2,656us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_ConsolidatedPropertyAndCasualtyInsuranceEntityMember |
| Life Insurance Segment                                                          |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Identifiable assets                                                             | 1,306us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                          | 1,316us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember |
| Investments Segment                                                             |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Identifiable assets                                                             | 14,544us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                          | 14,441us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember |
| Operating Segments | Commercial Lines                                           |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Earned premiums                                                                 | 733us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember                                                                                          | 692us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember                                                                                         |   |
| Fee revenues                                                                    | 1us-gaap_FeesAndCommissions/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember                                                                                           | 1us-gaap_FeesAndCommissions/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember                                                                                          |   |
| Revenues                                                                        | 734us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember                                                                                                   | 693us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember                                                                                                  |   |
| Income (loss) before income taxes                                               | 26us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 2us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |   |
| Operating Segments | Personal Lines                                             |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Earned premiums                                                                 | 268us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember                                                                                            | 254us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember                                                                                           |   |
| Fee revenues                                                                    | 1us-gaap_FeesAndCommissions/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember                                                                                             | 0us-gaap_FeesAndCommissions/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember                                                                                            |   |
| Revenues                                                                        | 269us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember                                                                                                     | 254us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember                                                                                                    |   |
| Income (loss) before income taxes                                               | (3)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember  | (7)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |   |
| Operating Segments | Excess and Surplus Lines Insurance                         |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Earned premiums                                                                 | 40us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessandSurplusLinesInsuranceMember                                                                                                                 | 33us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessandSurplusLinesInsuranceMember                                                                                                                |   |
| Income (loss) before income taxes                                               | 4us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessandSurplusLinesInsuranceMember                        | 4us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessandSurplusLinesInsuranceMember                       |   |
| Operating Segments | Life Insurance Segment                                     |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Earned premiums                                                                 | 53us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember                                                                                                                        | 48us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember                                                                                                                       |   |
| Fee revenues                                                                    | 1us-gaap_FeesAndCommissions/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember                                                                                                                        | 2us-gaap_FeesAndCommissions/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember                                                                                                                       |   |
| Revenues                                                                        | 54us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember                                                                                                                                 | 50us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember                                                                                                                                |   |
| Income (loss) before income taxes                                               | (3)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember                             | 0us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember                              |   |
| Operating Segments | Investments Segment                                        |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Investment income, net of expenses                                              | 139us-gaap_NetInvestmentIncome/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember                                                                                                                       | 135us-gaap_NetInvestmentIncome/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember                                                                                                                      |   |
| Realized investment gains, net                                                  | 47us-gaap_RealizedInvestmentGainsLosses/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember                                                                                                              | 22us-gaap_RealizedInvestmentGainsLosses/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember                                                                                                             |   |
| Revenues                                                                        | 186us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember                                                                                                                                  | 157us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember                                                                                                                                 |   |
| Income (loss) before income taxes                                               | 165us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember                               | 136us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember                              |   |
| Corporate and Other Non-Segment                                                 |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Other                                                                           | 2us-gaap_OtherIncome/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember                                                                                                                                                                                                   | 2us-gaap_OtherIncome/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember                                                                                                                                                                                                  |   |
| Income (loss) before income taxes                                               | (15)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember                                                                                                | (16)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember                                                                                               |   |
| Identifiable assets                                                             | 336us-gaap_Assets/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                          | 340us-gaap_Assets/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember |
| Commercial Casualty | Operating Segments | Commercial Lines                     |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Earned premiums                                                                 | 244us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_CommercialCasualtySegmentMember                           | 224us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_CommercialCasualtySegmentMember                          |   |
| Commercial Property | Operating Segments | Commercial Lines                     |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Earned premiums                                                                 | 196us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_CommercialPropertySegmentMember                           | 171us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_CommercialPropertySegmentMember                          |   |
| Commercial Auto | Operating Segments | Commercial Lines                         |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Earned premiums                                                                 | 136us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_CommercialAutoSegmentMember                               | 126us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_CommercialAutoSegmentMember                              |   |
| Workers' Compensation | Operating Segments | Commercial Lines                   |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Earned premiums                                                                 | 93us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_WorkersCompensationMember                                  | 92us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_WorkersCompensationMember                                 |   |
| Other Commercial Lines | Operating Segments | Commercial Lines                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Earned premiums                                                                 | 64us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_OtherCommercialLinesMember                                 | 79us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_OtherCommercialLinesMember                                |   |
| Personal Auto | Operating Segments | Personal Lines                             |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Earned premiums                                                                 | 123us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_PersonalAutoMember                                          | 116us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_PersonalAutoMember                                         |   |
| Home Owner Segment | Operating Segments | Personal Lines                        |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Earned premiums                                                                 | 114us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_HomeOwnerSegmentMember                                      | 109us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_HomeOwnerSegmentMember                                     |   |
| Other Personal Lines | Operating Segments | Personal Lines                      |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| **Segment Reporting Information [Line Items]**                                  |                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                          |   |
| Earned premiums                                                                 | $ 31us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_OtherPersonalLinesMember                                   | $ 29us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember/ us-gaap_SubsegmentsAxis= cinf_OtherPersonalLinesMember                                  |   |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.18) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 12 -Article 7Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 18 -Article 5
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of fees and commissions from financial services and banking activities and correspondent clearing. Includes fees from depositor accounts, credit cards, merchant discounts, and fiduciary and trust activities, guarantee fees, investment advisory, management, and administrative fees, transfer agent fees, and insurance commissions.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.13) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 13 -Article 9
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investments, income taxes, extraordinary items, and noncontrolling interest.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)(1)(i)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.
+ References
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| - Definition
Reflects the sum of all other revenue and income recognized by the entity in the period not otherwise specified in the income statement.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned.
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| - Definition
The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.
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| - Definition
Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).
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