| **Segment Information (Details) (USD $)In Millions, unless otherwise specified** | 3 Months Ended                                                                                                           | 12 Months Ended                                                                                                        |
|----------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------|
||
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Earned premiums                                                                  |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | $ 4,243us-gaap_PremiumsEarnedNet | $ 3,902us-gaap_PremiumsEarnedNet | $ 3,522us-gaap_PremiumsEarnedNet |
| Revenues                                                                         | 1,262us-gaap_Revenues                                                                                                    | 1,280us-gaap_Revenues                                                                                                  | 1,214us-gaap_Revenues | 1,189us-gaap_Revenues | 1,172us-gaap_Revenues | 1,152us-gaap_Revenues | 1,104us-gaap_Revenues | 1,103us-gaap_Revenues | 4,945us-gaap_Revenues | 4,531us-gaap_Revenues | 4,111us-gaap_Revenues |
| Other Income                                                                     |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 8us-gaap_OtherIncome | 9us-gaap_OtherIncome | 10us-gaap_OtherIncome |
| Fees and Commissions                                                             |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 12us-gaap_FeesAndCommissions | 8us-gaap_FeesAndCommissions | 6us-gaap_FeesAndCommissions |
| Net Investment Income                                                            |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 549us-gaap_NetInvestmentIncome | 529us-gaap_NetInvestmentIncome | 531us-gaap_NetInvestmentIncome |
| Realized investment gains, net                                                   |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 133us-gaap_RealizedInvestmentGainsLosses | 83us-gaap_RealizedInvestmentGainsLosses | 42us-gaap_RealizedInvestmentGainsLosses |
| Income before income taxes                                                       | 236us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments   | 259us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments | 107us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments | 119us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments | 167us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments | 182us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments | 148us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments | 217us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments | 721us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments | 714us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments | 566us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments |
| Identifiable assets                                                              | 18,753us-gaap_Assets                                                                                                     |                                                                                                                   |   |   | 17,662us-gaap_Assets |   |   |   | 18,753us-gaap_Assets | 17,662us-gaap_Assets |   |
| Number of Industries Operated In                                                 |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 2cinf_NumberofIndustriesOperatedIn |   |   |
| Number of Insurance Segments                                                     |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 4cinf_NumberofInsuranceSegments |   |   |
| Life Insurance Segment                                                           |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Earned premiums                                                                  |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 198us-gaap_PremiumsEarnedNet/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember | 189us-gaap_PremiumsEarnedNet/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember | 178us-gaap_PremiumsEarnedNet/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember |
| Identifiable assets                                                              | 1,316us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember                           |                                                                                                                   |   |   | 1,225us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember |   |   |   | 1,316us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember | 1,225us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember |   |
| Investments Segment                                                              |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Identifiable assets                                                              | 14,441us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember                            |                                                                                                                   |   |   | 13,618us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember |   |   |   | 14,441us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember | 13,618us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember |   |
| Consolidated Property and Casualty Insurance Entity                              |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Identifiable assets                                                              | 2,656us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_ConsolidatedPropertyAndCasualtyInsuranceEntityMember |                                                                                                                   |   |   | 2,455us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_ConsolidatedPropertyAndCasualtyInsuranceEntityMember |   |   |   | 2,656us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_ConsolidatedPropertyAndCasualtyInsuranceEntityMember | 2,455us-gaap_Assets/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_ConsolidatedPropertyAndCasualtyInsuranceEntityMember |   |
| Corporate and Other Non-Segment                                                  |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Other Income                                                                     |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 8us-gaap_OtherIncome/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember | 9us-gaap_OtherIncome/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember | 9us-gaap_OtherIncome/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember |
| Income before income taxes                                                       |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | (59)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember | (60)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember | (59)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember |
| Identifiable assets                                                              | 340us-gaap_Assets/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember                                |                                                                                                                   |   |   | 364us-gaap_Assets/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember |   |   |   | 340us-gaap_Assets/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember | 364us-gaap_Assets/ us-gaap_ConsolidationItemsAxis= cinf_CorporateandOtherNonSegmentMember |   |
| Operating Segments | Commercial Insurance                                        |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Earned premiums                                                                  |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 2,856us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 2,636us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 2,383us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Revenues                                                                         |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 2,860us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 2,639us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 2,387us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Fees and Commissions                                                             |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 4us-gaap_FeesAndCommissions/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 3us-gaap_FeesAndCommissions/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 4us-gaap_FeesAndCommissions/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Income before income taxes                                                       |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 146us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 186us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 181us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Operating Segments | Commercial Insurance | Commercial Casualty Line             |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Earned premiums                                                                  |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 938us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_CommercialCasualtySegmentMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 856us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_CommercialCasualtySegmentMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 767us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_CommercialCasualtySegmentMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Operating Segments | Commercial Insurance | Commercial Property Line             |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Earned premiums                                                                  |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 728us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_CommercialPropertySegmentMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 623us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_CommercialPropertySegmentMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 545us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_CommercialPropertySegmentMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Operating Segments | Commercial Insurance | Commercial Auto Line                 |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Earned premiums                                                                  |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 528us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_CommercialAutoSegmentMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 479us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_CommercialAutoSegmentMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 426us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_CommercialAutoSegmentMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Operating Segments | Commercial Insurance | Workers' Compensation Line           |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Earned premiums                                                                  |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 370us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_WorkersCompensationMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 365us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_WorkersCompensationMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 344us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_WorkersCompensationMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Operating Segments | Commercial Insurance | Other Commercial Lines               |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Earned premiums                                                                  |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 292us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_OtherCommercialLinesMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 313us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_OtherCommercialLinesMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 301us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_OtherCommercialLinesMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember |
| Operating Segments | Personal Insurance                                          |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Earned premiums                                                                  |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 1,041us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 961us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 868us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Revenues                                                                         |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 1,043us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 962us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 870us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Fees and Commissions                                                             |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 2us-gaap_FeesAndCommissions/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 1us-gaap_FeesAndCommissions/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 2us-gaap_FeesAndCommissions/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Income before income taxes                                                       |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 10us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 33us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | (43)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Operating Segments | Personal Insurance | Personal Auto                          |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Earned premiums                                                                  |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 476us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_PersonalAutoMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 443us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_PersonalAutoMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 404us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_PersonalAutoMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Operating Segments | Personal Insurance | Home Owner Line                        |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Earned premiums                                                                  |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 443us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_HomeOwnerSegmentMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 403us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_HomeOwnerSegmentMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 353us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_HomeOwnerSegmentMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Operating Segments | Personal Insurance | Other Personal Lines                   |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Earned premiums                                                                  |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 122us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_OtherPersonalLinesMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 115us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_OtherPersonalLinesMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 111us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_ProductOrServiceAxis= cinf_OtherPersonalLinesMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember |
| Operating Segments | Excess and Surplus Lines Insurance                          |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Earned premiums                                                                  |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 148us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessandSurplusLinesInsuranceMember | 116us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessandSurplusLinesInsuranceMember | 93us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessandSurplusLinesInsuranceMember |
| Income before income taxes                                                       |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 30us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessandSurplusLinesInsuranceMember | 14us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessandSurplusLinesInsuranceMember | (1)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= cinf_ExcessandSurplusLinesInsuranceMember |
| Operating Segments | Life Insurance Segment                                      |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Earned premiums                                                                  |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 198us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember | 189us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember | 178us-gaap_PremiumsEarnedNet/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember |
| Revenues                                                                         |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 204us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember | 193us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember | 179us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember |
| Fees and Commissions                                                             |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 6us-gaap_FeesAndCommissions/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember | 4us-gaap_FeesAndCommissions/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember | 1us-gaap_FeesAndCommissions/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember |
| Income before income taxes                                                       |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | (5)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember | 9us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember | (3)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_LifeInsuranceSegmentMember |
| Operating Segments | Investments Segment                                         |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| **Segment Reporting Information**                                                |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   |   |   |   |
| Revenues                                                                         |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 682us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember | 612us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember | 573us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember |
| Net Investment Income                                                            |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 549us-gaap_NetInvestmentIncome/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember | 529us-gaap_NetInvestmentIncome/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember | 531us-gaap_NetInvestmentIncome/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember |
| Realized investment gains, net                                                   |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | 133us-gaap_RealizedInvestmentGainsLosses/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember | 83us-gaap_RealizedInvestmentGainsLosses/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember | 42us-gaap_RealizedInvestmentGainsLosses/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember |
| Income before income taxes                                                       |                                                                                                                     |                                                                                                                   |   |   |   |   |   |   | $ 599us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember | $ 532us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember | $ 491us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments/ us-gaap_ConsolidationItemsAxis= us-gaap_OperatingSegmentsMember/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_InvestmentsSegmentMember |

| X                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Number of Industries Operated In
+ References
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| - Definition
Number of Insurance Segments
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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.
+ References
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned.
+ References
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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.
+ References
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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).
+ References
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