| **Shareholders' Equity And Dividend Restrictions (Change In AOCI Includes Changes In Unrealized Gains And Losses On Investments And Pension Obligations) (Details) (USD $)In Millions, unless otherwise specified** | 12 Months Ended                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Accumulated Other Comprehensive Income, Before Tax**                                                                                                                                                              |                                                                                                                                                                                                        |   |   |
| Pension obligations OCI                                                                                                                                                                                             | $ (18)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax                                                                                                      | $ 83us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax | $ (13)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax |
| **Accumulated Other Comprehensive Income, Income Tax**                                                                                                                                                              |                                                                                                                                                                                                        |   |   |
| Income taxes on above of other comprehensive income                                                                                                                                                                 | 130us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1                                                                                                                                      | 202us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1 | 124us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1 |
| **Accumulated Other Comprehensive Income, Net of Tax**                                                                                                                                                              |                                                                                                                                                                                                        |   |   |
| AOCI, balance at the beginning of the period                                                                                                                                                                        | 1,504us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax                                                                                                                                                |   |   |
| Other comprehensive income before tax                                                                                                                                                                               | 370us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent                                                                                                                                  | 577us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent | 352us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent |
| AOCI, balance at the end of the period                                                                                                                                                                              | 1,744us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax                                                                                                                                                | 1,504us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax |   |
| Accumulated Net Unrealized Investment Gain (Loss)                                                                                                                                                                   |                                                                                                                                                                                                        |   |   |
| **Accumulated Other Comprehensive Income, Before Tax**                                                                                                                                                              |                                                                                                                                                                                                        |   |   |
| AOCI, balance at the beginning of the period                                                                                                                                                                        | 2,335us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember                                             | 1,875us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember | 1,489us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember |
| OCI before realized gains (losses) recognized in net income                                                                                                                                                         | 514us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember                                    | 537us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember | 426us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember |
| Realized gains (losses) recognized in net income                                                                                                                                                                    | (130)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember                 | (77)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember | (40)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember |
| OCI, portion attributable to Parent                                                                                                                                                                                 | 384us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember                                | 460us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember | 386us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember |
| AOCI, balance at the end of the period                                                                                                                                                                              | 2,719us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember                                             | 2,335us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember | 1,875us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember |
| **Accumulated Other Comprehensive Income, Income Tax**                                                                                                                                                              |                                                                                                                                                                                                        |   |   |
| AOCI, balance at the beginning of the period                                                                                                                                                                        | 808cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember                                                         | 647cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember | 512cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember |
| OCI before realized gains (losses) recognized in net income                                                                                                                                                         | 181cinf_OtherComprehensiveIncomeLossBeforeReclassificationsTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember                                             | 188cinf_OtherComprehensiveIncomeLossBeforeReclassificationsTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember | 149cinf_OtherComprehensiveIncomeLossBeforeReclassificationsTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember |
| Realized gains (losses) recognized in net income                                                                                                                                                                    | (47)cinf_ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember                           | (27)cinf_ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember | (14)cinf_ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember |
| Income taxes on above of other comprehensive income                                                                                                                                                                 | 134us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember                                     | 161us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember | 135us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember |
| AOCI, balance at the end of the period                                                                                                                                                                              | 942cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember                                                         | 808cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember | 647cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember |
| **Accumulated Other Comprehensive Income, Net of Tax**                                                                                                                                                              |                                                                                                                                                                                                        |   |   |
| AOCI, balance at the beginning of the period                                                                                                                                                                        | 1,527us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember                                               | 1,228us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember | 977us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember |
| OCI before realized gains (losses) recognized in net income                                                                                                                                                         | 333us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember                                     | 349us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember | 277us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember |
| Realized gains (losses) recognized in net income                                                                                                                                                                    | (83)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember                   | (50)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember | (26)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember |
| Other comprehensive income before tax                                                                                                                                                                               | 250us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember                                 | 299us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember | 251us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember |
| AOCI, balance at the end of the period                                                                                                                                                                              | 1,777us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember                                               | 1,527us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember | 1,228us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember |
| Accumulated Defined Benefit Plans Adjustment                                                                                                                                                                        |                                                                                                                                                                                                        |   |   |
| **Accumulated Other Comprehensive Income, Before Tax**                                                                                                                                                              |                                                                                                                                                                                                        |   |   |
| AOCI, balance at the beginning of the period                                                                                                                                                                        | (18)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember                                                | (101)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | (88)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
| OCI before realized gains (losses) recognized in net income                                                                                                                                                         | (21)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember                                     | 83us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | (13)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
| Realized gains (losses) recognized in net income                                                                                                                                                                    | 3us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember                       | 0us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | 0us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
| OCI, portion attributable to Parent                                                                                                                                                                                 | (18)us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember                                 | 83us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | (13)us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
| AOCI, balance at the end of the period                                                                                                                                                                              | (36)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember                                                | (18)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | (101)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
| **Accumulated Other Comprehensive Income, Income Tax**                                                                                                                                                              |                                                                                                                                                                                                        |   |   |
| AOCI, balance at the beginning of the period                                                                                                                                                                        | (6)cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember                                                           | (35)cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | (31)cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
| OCI before realized gains (losses) recognized in net income                                                                                                                                                         | (7)cinf_OtherComprehensiveIncomeLossBeforeReclassificationsTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember                                               | 29cinf_OtherComprehensiveIncomeLossBeforeReclassificationsTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | (4)cinf_OtherComprehensiveIncomeLossBeforeReclassificationsTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
| Realized gains (losses) recognized in net income                                                                                                                                                                    | 1cinf_ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember                                | 0cinf_ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | 0cinf_ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
| Income taxes on above of other comprehensive income                                                                                                                                                                 | (6)us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember                                       | 29us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | (4)us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
| AOCI, balance at the end of the period                                                                                                                                                                              | (12)cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember                                                          | (6)cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | (35)cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
| **Accumulated Other Comprehensive Income, Net of Tax**                                                                                                                                                              |                                                                                                                                                                                                        |   |   |
| AOCI, balance at the beginning of the period                                                                                                                                                                        | (12)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember                                                  | (66)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | (57)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
| OCI before realized gains (losses) recognized in net income                                                                                                                                                         | (14)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember                                      | 54us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | (9)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
| Realized gains (losses) recognized in net income                                                                                                                                                                    | 2us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember                        | 0us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | 0us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
| Other comprehensive income before tax                                                                                                                                                                               | (12)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember                                  | 54us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | (9)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
| AOCI, balance at the end of the period                                                                                                                                                                              | (24)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember                                                  | (12)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | (66)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
| Accumulated Net Unrealized Gain (Loss) on Deferred Costs, Reserves And Other                                                                                                                                        |                                                                                                                                                                                                        |   |   |
| **Accumulated Other Comprehensive Income, Before Tax**                                                                                                                                                              |                                                                                                                                                                                                        |   |   |
| AOCI, balance at the beginning of the period                                                                                                                                                                        | (16)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember                            | (50)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | (29)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember |
| OCI before realized gains (losses) recognized in net income                                                                                                                                                         | 7us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember                    | 40us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | (19)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember |
| Realized gains (losses) recognized in net income                                                                                                                                                                    | (3)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | (6)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | (2)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember |
| OCI, portion attributable to Parent                                                                                                                                                                                 | 4us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember                | 34us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | (21)us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember |
| AOCI, balance at the end of the period                                                                                                                                                                              | (12)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember                            | (16)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | (50)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember |
| **Accumulated Other Comprehensive Income, Income Tax**                                                                                                                                                              |                                                                                                                                                                                                        |   |   |
| AOCI, balance at the beginning of the period                                                                                                                                                                        | (5)cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember                                       | (17)cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | (10)cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember |
| OCI before realized gains (losses) recognized in net income                                                                                                                                                         | 3cinf_OtherComprehensiveIncomeLossBeforeReclassificationsTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember                             | 14cinf_OtherComprehensiveIncomeLossBeforeReclassificationsTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | (7)cinf_OtherComprehensiveIncomeLossBeforeReclassificationsTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember |
| Realized gains (losses) recognized in net income                                                                                                                                                                    | (1)cinf_ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember          | (2)cinf_ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | 0cinf_ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember |
| Income taxes on above of other comprehensive income                                                                                                                                                                 | 2us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember                     | 12us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | (7)us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember |
| AOCI, balance at the end of the period                                                                                                                                                                              | (3)cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember                                       | (5)cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | (17)cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember |
| **Accumulated Other Comprehensive Income, Net of Tax**                                                                                                                                                              |                                                                                                                                                                                                        |   |   |
| AOCI, balance at the beginning of the period                                                                                                                                                                        | (11)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember                              | (33)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | (19)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember |
| OCI before realized gains (losses) recognized in net income                                                                                                                                                         | 4us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember                     | 26us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | (12)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember |
| Realized gains (losses) recognized in net income                                                                                                                                                                    | (2)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember  | (4)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | (2)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember |
| Other comprehensive income before tax                                                                                                                                                                               | 2us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember                 | 22us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | (14)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember |
| AOCI, balance at the end of the period                                                                                                                                                                              | (9)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember                               | (11)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember | (33)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember |
| Accumulated Other Comprehensive Income (Loss)                                                                                                                                                                       |                                                                                                                                                                                                        |   |   |
| **Accumulated Other Comprehensive Income, Before Tax**                                                                                                                                                              |                                                                                                                                                                                                        |   |   |
| AOCI, balance at the beginning of the period                                                                                                                                                                        | 2,301us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember                                                    | 1,724us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | 1,372us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| Investments OCI                                                                                                                                                                                                     | 384cinf_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAndOtherAssetsAdjustmentBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember                   | 460cinf_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAndOtherAssetsAdjustmentBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | 386cinf_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAndOtherAssetsAdjustmentBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| Pension obligations OCI                                                                                                                                                                                             | (18)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember              | 83us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | (13)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| Life deferred acquisition costs, life policy reserves and other OCI                                                                                                                                                 | 4cinf_OtherComprehensiveIncomeLossDeferredAcquisitionCostsLifePolicyReservesAndOtherAdjustmentBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember           | 34cinf_OtherComprehensiveIncomeLossDeferredAcquisitionCostsLifePolicyReservesAndOtherAdjustmentBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | (21)cinf_OtherComprehensiveIncomeLossDeferredAcquisitionCostsLifePolicyReservesAndOtherAdjustmentBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| Total OCI                                                                                                                                                                                                           | 370cinf_IncreaseDecreaseInOtherComprehensiveIncomeLossBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember                                                   | 577cinf_IncreaseDecreaseInOtherComprehensiveIncomeLossBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | 352cinf_IncreaseDecreaseInOtherComprehensiveIncomeLossBeforeTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| AOCI, balance at the end of the period                                                                                                                                                                              | 2,671us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember                                                    | 2,301us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | 1,724us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| **Accumulated Other Comprehensive Income, Income Tax**                                                                                                                                                              |                                                                                                                                                                                                        |   |   |
| AOCI, balance at the beginning of the period                                                                                                                                                                        | 797cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember                                                                | 595cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | 471cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| Investments OCI                                                                                                                                                                                                     | 134cinf_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAndOtherAssetsAdjustmentTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember                         | 161cinf_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAndOtherAssetsAdjustmentTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | 135cinf_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAndOtherAssetsAdjustmentTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| Pension obligations OCI                                                                                                                                                                                             | (6)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember                               | 29us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | (4)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| Life deferred acquisition costs, life policy reserves and other OCI                                                                                                                                                 | 2cinf_OtherComprehensiveIncomeLossDeferredAcquisitionCostsLifePolicyReservesAndOtherAdjustmentTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember                 | 12cinf_OtherComprehensiveIncomeLossDeferredAcquisitionCostsLifePolicyReservesAndOtherAdjustmentTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | (7)cinf_OtherComprehensiveIncomeLossDeferredAcquisitionCostsLifePolicyReservesAndOtherAdjustmentTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| Total OCI                                                                                                                                                                                                           | 130cinf_IncreaseDecreaseInOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember                                                         | 202cinf_IncreaseDecreaseInOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | 124cinf_IncreaseDecreaseInOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| AOCI, balance at the end of the period                                                                                                                                                                              | 927cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember                                                                | 797cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | 595cinf_AccumulatedOtherComprehensiveIncomeLossTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| **Accumulated Other Comprehensive Income, Net of Tax**                                                                                                                                                              |                                                                                                                                                                                                        |   |   |
| AOCI, balance at the beginning of the period                                                                                                                                                                        | 1,504us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember                                                      | 1,129us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | 901us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| Investments OCI                                                                                                                                                                                                     | 250cinf_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAndOtherAssetsAdjustmentNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember                    | 299cinf_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAndOtherAssetsAdjustmentNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | 251cinf_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAndOtherAssetsAdjustmentNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| Pension obligations OCI                                                                                                                                                                                             | (12)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember               | 54us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | (9)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| Life deferred acquisition costs, life policy reserves and other OCI                                                                                                                                                 | 2cinf_OtherComprehensiveIncomeLossDeferredAcquisitionCostsLifePolicyReservesAndOtherAdjustmentNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember            | 22cinf_OtherComprehensiveIncomeLossDeferredAcquisitionCostsLifePolicyReservesAndOtherAdjustmentNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | (14)cinf_OtherComprehensiveIncomeLossDeferredAcquisitionCostsLifePolicyReservesAndOtherAdjustmentNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| Total OCI                                                                                                                                                                                                           | 240cinf_IncreaseDecreaseInOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember                                                    | 375cinf_IncreaseDecreaseInOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | 228cinf_IncreaseDecreaseInOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |
| AOCI, balance at the end of the period                                                                                                                                                                              | $ 1,744us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember                                                    | $ 1,504us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember | $ 1,129us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax/ us-gaap_StatementEquityComponentsAxis= us-gaap_AccumulatedOtherComprehensiveIncomeMember |

| X                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Accumulated Other Comprehensive Income (Loss), Tax
+ References
No definition available.
+ Details**Name:**cinf_AccumulatedOtherComprehensiveIncomeLossTax**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**cinf_AccumulatedOtherComprehensiveIncomeLossTaxAbstract**Namespace Prefix:**cinf_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**cinf_AccumulatedOtherComprehensiveIncomeRollForward**Namespace Prefix:**cinf_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Increase (Decrease) in Other Comprehensive Income (Loss), before Tax
+ References
No definition available.
+ Details**Name:**cinf_IncreaseDecreaseInOtherComprehensiveIncomeLossBeforeTax**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Increase (Decrease) in Other Comprehensive Income (Loss), Net of Tax
+ References
No definition available.
+ Details**Name:**cinf_IncreaseDecreaseInOtherComprehensiveIncomeLossNetOfTax**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Increase (Decrease) in Other Comprehensive Income (Loss), Tax
+ References
No definition available.
+ Details**Name:**cinf_IncreaseDecreaseInOtherComprehensiveIncomeLossTax**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Other Comprehensive Income (Loss), Available-for-sale Securities and Other Assets Adjustment, before Tax
+ References
No definition available.
+ Details**Name:**cinf_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAndOtherAssetsAdjustmentBeforeTax**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Other Comprehensive Income (Loss), Available-for-sale Securities and Other Assets Adjustment, Net of Tax
+ References
No definition available.
+ Details**Name:**cinf_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAndOtherAssetsAdjustmentNetOfTax**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Other Comprehensive Income (Loss), Available-for-sale Securities and Other Assets Adjustment, Tax
+ References
No definition available.
+ Details**Name:**cinf_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAndOtherAssetsAdjustmentTax**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Other Comprehensive Income (Loss), Before Reclassifications, Tax
+ References
No definition available.
+ Details**Name:**cinf_OtherComprehensiveIncomeLossBeforeReclassificationsTax**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Other Comprehensive Income (Loss), Deferred Acquisition Costs, Life Policy Reserves and Other Adjustment, before Tax
+ References
No definition available.
+ Details**Name:**cinf_OtherComprehensiveIncomeLossDeferredAcquisitionCostsLifePolicyReservesAndOtherAdjustmentBeforeTax**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Other Comprehensive Income (Loss), Deferred Acquisition Costs, Life Policy Reserves and Other Adjustment, Net of Tax
+ References
No definition available.
+ Details**Name:**cinf_OtherComprehensiveIncomeLossDeferredAcquisitionCostsLifePolicyReservesAndOtherAdjustmentNetOfTax**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Other Comprehensive Income (Loss), Deferred Acquisition Costs, Life Policy Reserves and Other Adjustment, Tax
+ References
No definition available.
+ Details**Name:**cinf_OtherComprehensiveIncomeLossDeferredAcquisitionCostsLifePolicyReservesAndOtherAdjustmentTax**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Reclassification from Accumulated Other Comprehensive Income, Current Period, Tax
+ References
No definition available.
+ Details**Name:**cinf_ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodTax**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before tax of increase (decrease) in accumulated in equity from transactions and other events and circumstances from non-owner sources. Excludes net income (loss), and accumulated changes in equity from transactions resulting from investments by owners (distributions to owners).
+ References
No definition available.
+ Details**Name:**us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e681-108580Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669686-108580Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 31 -Article 5Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3
+ Details**Name:**us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before tax and reclassification adjustments of other comprehensive income (loss).
+ References
No definition available.
+ Details**Name:**us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount after tax, before reclassification adjustments of other comprehensive income (loss).
+ References
No definition available.
+ Details**Name:**us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before tax of other comprehensive income (loss) attributable to parent entity.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=7656940&loc=SL4569643-111683Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 19 -URI http://asc.fasb.org/extlink&oid=7656940&loc=SL4569616-111683Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=18733093&loc=SL4573702-111684
+ Details**Name:**us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount after tax of other comprehensive income (loss) attributable to parent entity.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=7656940&loc=SL4569643-111683Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 19 -URI http://asc.fasb.org/extlink&oid=7656940&loc=SL4569616-111683Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=18733093&loc=SL4573702-111684
+ Details**Name:**us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before tax, after reclassification adjustments, of (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i-k) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580
+ Details**Name:**us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount after tax and reclassification adjustments, of (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i-k) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580
+ Details**Name:**us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of tax (expense) benefit, after reclassification adjustments, of (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e640-108580Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i-k) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580
+ Details**Name:**us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of tax expense (benefit) allocated to other comprehensive income (loss) attributable to parent entity.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=7656940&loc=SL4569643-111683Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 19 -URI http://asc.fasb.org/extlink&oid=7656940&loc=SL4569616-111683Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=18733093&loc=SL4573702-111684
+ Details**Name:**us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before tax of reclassification adjustments of other comprehensive income (loss).
+ References
No definition available.
+ Details**Name:**us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount after tax of reclassification adjustments of other comprehensive income (loss).
+ References
No definition available.
+ Details**Name:**us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementEquityComponentsAxis=cinf_AccumulatedNetUnrealizedGainLossOnDeferredCostsReservesAndOtherMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                    |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedOtherComprehensiveIncomeMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |