| **Employee Retirement Benefits (Narrative) (Details) (USD $)In Millions, except Share data, unless otherwise specified** | 12 Months Ended                                                                                                                                                                                                                                                 | 3 Months Ended                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Minimum participant age to elect                                                                                         |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   | 40 years |   |   |
| Employer discretionary contribution amount                                                                               | $ 11us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount                                                                                                                                                                                      | $ 10us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount                                                                                                                                                      | $ 9us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount |   |   |   |
| Requisite service period                                                                                                 | 3 years                                                                                                                                                                                                                                                         |                                                                                                                                                                                                                            |   |   |   |   |
| Actual return on plan assets                                                                                             | 11.70%cinf_DefinedBenefitPlanActualPercentageReturnOnPlanAssets                                                                                                                                                                                                 | 24.00%cinf_DefinedBenefitPlanActualPercentageReturnOnPlanAssets                                                                                                                                                                 |   |   |   |   |
| Total recognized in net periodic benefit cost and other comprehensive income                                             | (31)cinf_DefinedBenefitPlanTotalRecognizedInNetPeriodicBenefitCostsAndOtherComprehensiveIncomeBeforeTax                                                                                                                                                         | 63cinf_DefinedBenefitPlanTotalRecognizedInNetPeriodicBenefitCostsAndOtherComprehensiveIncomeBeforeTax                                                                                                                           | (31)cinf_DefinedBenefitPlanTotalRecognizedInNetPeriodicBenefitCostsAndOtherComprehensiveIncomeBeforeTax |   |   |   |
| Amortization of actuarial loss                                                                                           | 5us-gaap_DefinedBenefitPlanFutureAmortizationOfGainLoss                                                                                                                                                                                                         |                                                                                                                                                                                                                            |   |   |   |   |
| Amortization of prior service cost                                                                                       | 1us-gaap_DefinedBenefitPlanFutureAmortizationOfPriorServiceCostCredit                                                                                                                                                                                           |                                                                                                                                                                                                                            |   |   |   |   |
| Pension plan assets at fair value                                                                                        | 288us-gaap_DefinedBenefitPlanFairValueOfPlanAssets                                                                                                                                                                                                              | 280us-gaap_DefinedBenefitPlanFairValueOfPlanAssets                                                                                                                                                                              | 238us-gaap_DefinedBenefitPlanFairValueOfPlanAssets |   |   |   |
| Cash dividends paid                                                                                                      | 288us-gaap_DividendsCommonStockCash                                                                                                                                                                                                                             | 270us-gaap_DividendsCommonStockCash                                                                                                                                                                                             | 263us-gaap_DividendsCommonStockCash |   |   |   |
| Domestic Equity Securities                                                                                               |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Allocation percentage of investments                                                                                     | 81.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= cinf_DomesticEquitySecuritiesMember                                                                                                |                                                                                                                                                                                                                            |   |   |   |   |
| Domestic Equity Securities | Information Technology Sector                                                               |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Allocation percentage of investments                                                                                     | 19.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations/ cinf_DefinedBenefitPlanAssetAllocationsAxis= cinf_InformationSystemsAndTechnologyMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= cinf_DomesticEquitySecuritiesMember       |                                                                                                                                                                                                                            |   |   |   |   |
| Domestic Equity Securities | Financial Services Sector                                                                   |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Allocation percentage of investments                                                                                     | 23.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations/ cinf_DefinedBenefitPlanAssetAllocationsAxis= cinf_FinancialServicesSectorMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= cinf_DomesticEquitySecuritiesMember               |                                                                                                                                                                                                                            |   |   |   |   |
| Domestic Equity Securities | Healthcare Sector                                                                           |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Allocation percentage of investments                                                                                     | 14.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations/ cinf_DefinedBenefitPlanAssetAllocationsAxis= cinf_HealthcareMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= cinf_DomesticEquitySecuritiesMember                            |                                                                                                                                                                                                                            |   |   |   |   |
| Domestic Equity Securities | Industrial Sector                                                                           |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Allocation percentage of investments                                                                                     | 12.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations/ cinf_DefinedBenefitPlanAssetAllocationsAxis= cinf_IndustrialSectorMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= cinf_DomesticEquitySecuritiesMember                      |                                                                                                                                                                                                                            |   |   |   |   |
| Domestic Equity Securities | All Remaining Sectors                                                                       |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Allocation percentage of investments                                                                                     | 10.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations/ cinf_DefinedBenefitPlanAssetAllocationsAxis= cinf_AllRemainingSectorsMember/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= cinf_DomesticEquitySecuritiesMember                   |                                                                                                                                                                                                                            |   |   |   |   |
| States, Municipalities and Political Subdivisions                                                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Allocation percentage of investments                                                                                     | 12.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_USStatesAndPoliticalSubdivisionsMember                                                                                     |                                                                                                                                                                                                                            |   |   |   |   |
| Domestic Corporate Debt Securities                                                                                       |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Allocation percentage of investments                                                                                     | 7.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_DomesticCorporateDebtSecuritiesMember                                                                                       |                                                                                                                                                                                                                            |   |   |   |   |
| Cash and Cash Equivalents                                                                                                |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Pension plan assets at fair value                                                                                        | 11us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CashAndCashEquivalentsMember                                                                                                             | 19us-gaap_DefinedBenefitPlanFairValueOfPlanAssets/ cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis= us-gaap_CashAndCashEquivalentsMember                                                                             |   |   |   |   |
| Maximum                                                                                                                  |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Matching contribution to defined contribution plan                                                                       | 6.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch/ us-gaap_RangeAxis= us-gaap_MaximumMember                                                                                                                                        |                                                                                                                                                                                                                            |   |   |   |   |
| Pension Plan                                                                                                             |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Pension plan assets, shares                                                                                              | 467,113us-gaap_DefinedBenefitPlanNumberOfSharesOfEquitySecuritiesIssuedByEmployerAndRelatedPartiesIncludedInPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                                 | 467,113us-gaap_DefinedBenefitPlanNumberOfSharesOfEquitySecuritiesIssuedByEmployerAndRelatedPartiesIncludedInPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember |   |   |   |   |
| Pension plan assets, fair value                                                                                          | 24us-gaap_DefinedBenefitPlanAmountOfEmployerAndRelatedPartySecuritiesIncludedInPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                                                              | 24us-gaap_DefinedBenefitPlanAmountOfEmployerAndRelatedPartySecuritiesIncludedInPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                              |   |   |   |   |
| Shares sold during period                                                                                                |                                                                                                                                                                                                                                                            | 100,000cinf_DefinedBenefitPlanCompanySharesSoldDuringPeriod/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                                                            |   |   |   |   |
| Pension plan assets, entity's shares sold, gain                                                                          |                                                                                                                                                                                                                                                            | 5cinf_Definedbenefitplanentitysharessoldrealizedgain/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                                                                   |   |   |   |   |
| Cash dividends paid                                                                                                      | 1us-gaap_DividendsCommonStockCash/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                                                                                                                      | 1us-gaap_DividendsCommonStockCash/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                                                                                      |   |   |   |   |
| Pension Plan | Benefit Obligations                                                                                       |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Percentage of increase decrease in discount rate                                                                         | 0.90%cinf_ChangeInDiscountRateAssumption/ cinf_DefinedBenefitPlanByBenefitPlanCategoriesAxis= cinf_BenefitObligationsMember/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                            |                                                                                                                                                                                                                            |   |   |   |   |
| Pension Plan | Net Periodic Benefit Costs                                                                                |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Percentage of increase decrease in discount rate                                                                         | 0.95%cinf_ChangeInDiscountRateAssumption/ cinf_DefinedBenefitPlanByBenefitPlanCategoriesAxis= cinf_NetPeriodicBenefitCostsMember/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember                       |                                                                                                                                                                                                                            |   |   |   |   |
| Supplemental Employee Retirement Plan                                                                                    |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Accrued employee benefit                                                                                                 | 13us-gaap_AccruedEmployeeBenefitsCurrentAndNoncurrent/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember                                                                            | 9us-gaap_AccruedEmployeeBenefitsCurrentAndNoncurrent/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember                                             |   |   |   |   |
| Supplemental Employee Retirement Plan | Forecast                                                                         |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Expected contribution by employer during 2015                                                                            |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   | 3us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember/ us-gaap_StatementScenarioAxis= us-gaap_ScenarioForecastMember |   |
| Supplemental Employee Retirement Plan | Benefit Obligations                                                              |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Percentage of increase decrease in discount rate                                                                         | 0.75%cinf_ChangeInDiscountRateAssumption/ cinf_DefinedBenefitPlanByBenefitPlanCategoriesAxis= cinf_BenefitObligationsMember/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember      |                                                                                                                                                                                                                            |   |   |   |   |
| Supplemental Employee Retirement Plan | Net Periodic Benefit Costs                                                       |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Percentage of increase decrease in discount rate                                                                         | 0.85%cinf_ChangeInDiscountRateAssumption/ cinf_DefinedBenefitPlanByBenefitPlanCategoriesAxis= cinf_NetPeriodicBenefitCostsMember/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |                                                                                                                                                                                                                            |   |   |   |   |
| Top Hat Savings Plan - Mutual Funds and Common Equities                                                                  |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| CFC Top Hat Savings Plan                                                                                                 | 18us-gaap_OtherInvestmentNotReadilyMarketableFairValue/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefitMember                                                                         | 14us-gaap_OtherInvestmentNotReadilyMarketableFairValue/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis= us-gaap_OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefitMember                                         |   |   |   |   |
| Subsequent Event | Pension Plan                                                                                          |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| **Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block**                                        |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   |   |
| Expected contribution by employer during 2015                                                                            |                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                            |   |   |   | $ 5us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= us-gaap_PensionPlansDefinedBenefitMember/ us-gaap_SubsequentEventTypeAxis= us-gaap_SubsequentEventMember |

| X                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Change in discount rate assumption.
+ References
No definition available.
+ Details**Name:**cinf_ChangeInDiscountRateAssumption**Namespace Prefix:**cinf_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Defined Benefit Plan, Actual Percentage Return On Plan Assets
+ References
No definition available.
+ Details**Name:**cinf_DefinedBenefitPlanActualPercentageReturnOnPlanAssets**Namespace Prefix:**cinf_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Defined Benefit Plan Company Shares Sold During Period
+ References
No definition available.
+ Details**Name:**cinf_DefinedBenefitPlanCompanySharesSoldDuringPeriod**Namespace Prefix:**cinf_**Data Type:**xbrli:sharesItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Defined benefit plan shares sold related to entity, gain.
+ References
No definition available.
+ Details**Name:**cinf_Definedbenefitplanentitysharessoldrealizedgain**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Age at which participants could elect to remain in the defined benefit plan as of August 31, 2008.
+ References
No definition available.
+ Details**Name:**cinf_DefinedBenefitPlanQualifyingAge**Namespace Prefix:**cinf_**Data Type:**xbrli:durationItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Defined Benefit Plan, Total Recognized in Net Periodic Benefit Costs and Other Comprehensive Income, before Tax
+ References
No definition available.
+ Details**Name:**cinf_DefinedBenefitPlanTotalRecognizedInNetPeriodicBenefitCostsAndOtherComprehensiveIncomeBeforeTax**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                    |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Defined Contribution Plan, Requisite Service Period
+ References
No definition available.
+ Details**Name:**cinf_DefinedContributionPlanRequisiteServicePeriod**Namespace Prefix:**cinf_**Data Type:**xbrli:durationItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Carrying value as of the balance sheet date of obligations, excluding pension and other postretirement benefits, incurred through that date and payable for perquisites provided to employees pertaining to services received from them.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.15(5)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.15(a)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 15 -Subparagraph a -Article 7Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 15 -Subparagraph 5 -Article 9
+ Details**Name:**us-gaap_AccruedEmployeeBenefitsCurrentAndNoncurrent**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of employer securities or securities of parties related to the employer that are included in plan assets.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (n) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920
+ Details**Name:**us-gaap_DefinedBenefitPlanAmountOfEmployerAndRelatedPartySecuritiesIncludedInPlanAssets**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Section 35 -Paragraph 50 -URI http://asc.fasb.org/extlink&oid=29635418&loc=d3e12355-114930
+ Details**Name:**us-gaap_DefinedBenefitPlanFairValueOfPlanAssets**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount included in accumulated other comprehensive income (AOCI) related to gain (loss) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position.
+ References
No definition available.
+ Details**Name:**us-gaap_DefinedBenefitPlanFutureAmortizationOfGainLoss**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount included in accumulated other comprehensive income (AOCI) related to prior service cost (credit) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position.
+ References
No definition available.
+ Details**Name:**us-gaap_DefinedBenefitPlanFutureAmortizationOfPriorServiceCostCredit**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The number of employer shares or related party shares included in plan assets.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (n) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920
+ Details**Name:**us-gaap_DefinedBenefitPlanNumberOfSharesOfEquitySecuritiesIssuedByEmployerAndRelatedPartiesIncludedInPlanAssets**Namespace Prefix:**us-gaap_**Data Type:**xbrli:sharesItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920
+ Details**Name:**us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2446-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920
+ Details**Name:**us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations**Namespace Prefix:**us-gaap_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of discretionary contributions made by an employer to a defined contribution plan.
+ References
No definition available.
+ Details**Name:**us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage employer matches of the employee's percentage contribution matched.
+ References
No definition available.
+ Details**Name:**us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch**Namespace Prefix:**us-gaap_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770
+ Details**Name:**us-gaap_DividendsCommonStockCash**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Value of the other investment not readily marketable determined by management based upon fair value methods, including pricing of similar securities and valuation techniques, that was used to record the investment for financial reporting purposes.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 820 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35710923&loc=d3e45360-110995
+ Details**Name:**us-gaap_OtherInvestmentNotReadilyMarketableFairValue**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis=cinf_DomesticEquitySecuritiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis=us-gaap_CashAndCashEquivalentsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis=us-gaap_DomesticCorporateDebtSecuritiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**cinf_DefinedBenefitPlanByPlanAssetsSecondaryCategoriesAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_PensionPlansDefinedBenefitMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefitMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_RangeAxis=us-gaap_MaximumMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |