| **Summary Of Significant Accounting Policies (Narrative) (Details)**                                                           | 12 Months Ended   |
|--------------------------------------------------------------------------------------------------------------------------------|-------------------|
||
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Unrealized gains reclassified to retained earnings for ASU 2016-01, after tax                                                  | $ 2,503,000,000   |   |   |   |
| Income Tax Examination, Penalties Expense                                                                                      | $ 0               |   |   |   |
| Number of operating subsidaries | subsidiary                                                                                   | 2                 |   |   |   |
| Number of independent insurance agencies | independent_insurance_agency                                                        | 1,757             |   |   |   |
| Number of reporting locations | reporting_locations                                                                            | 2,344             |   |   |   |
| Number of states in which entity operates | state                                                                              | 42                |   |   |   |
| Defined Benefit Plan Qualifying Age                                                                                            |              |   |   | 40 years |
| Current fair value of the BOLI invested assets and cash exceeded the current fair value of the contract holders' account value | $ 3,000,000       | $ 29,000,000 |   |   |
| Other invested assets                                                                                                          | 123,000,000       | 103,000,000 |   |   |
| Depreciation expense                                                                                                           | 31,000,000        | 28,000,000 | $ 30,000,000 |   |
| Land, building and equipment impairments                                                                                       | 0                 | 0 | 0 |   |
| Total                                                                                                                          | $ 402,000,000     | (148,000,000) | (124,000,000) |   |
| Minimum                                                                                                                        |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Estimated useful lives                                                                                                         | 3 years           |   |   |   |
| Maximum                                                                                                                        |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Estimated useful lives                                                                                                         | 39 years 6 months |   |   |   |
| Life Policy Loans                                                                                                              |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Other invested assets                                                                                                          | $ 33,000,000      | 31,000,000 |   |   |
| Venture Capital Funds                                                                                                          |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Other invested assets                                                                                                          | 60,000,000        | 35,000,000 |   |   |
| Real Estate Investment                                                                                                         |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Other invested assets                                                                                                          | $ 30,000,000      | $ 37,000,000 |   |   |
| 10 Largest States                                                                                                              |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Generated percentage of total earned premiums                                                                                  | 58.40%            | 59.70% |   |   |
| Ohio, Largest State                                                                                                            |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Generated percentage of total earned premiums                                                                                  | 15.90%            | 16.20% |   |   |
| Illinois, Georgia, Indiana, North Carolina and Pennsylvania | Minimum                                                          |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Generated percentage of total earned premiums                                                                                  | 5.00%             |   |   |   |
| Illinois, Georgia, Indiana, North Carolina and Pennsylvania | Maximum                                                          |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Generated percentage of total earned premiums                                                                                  | 6.00%             |   |   |   |
| Largest Single Agency Relationship                                                                                             |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Generated percentage of total earned premiums                                                                                  | 0.80%             |   |   |   |
| All Other | Maximum                                                                                                            |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Generated percentage of total earned premiums                                                                                  | 4.00%             |   |   |   |
| Stock Options                                                                                                                  |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Weighted-average remaining contractual life for options expected to vest                                                       | 10 years          |   |   |   |
| Property Casualty Insurance Segment                                                                                            |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Number of operating subsidaries | subsidiary                                                                                   | 2                 |   |   |   |
| Stock Options                                                                                                                  |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Awards vesting period                                                                                                          | 3 years           |   |   |   |
| Restricted Stock Units (RSUs)                                                                                                  |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Awards vesting period                                                                                                          | 3 years           |   |   |   |
| Equity Securities                                                                                                              |              |   |   |   |
| **Significant Accounting Policies**                                                                                            |              |   |   |   |
| Total                                                                                                                          | $ 395,000,000     | $ (120,000,000) | (99,000,000) |   |
| Unrealized Gain (Loss) on Investments                                                                                          | $ 404,000,000     | $ 0 | $ 0 |   |

| 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
Independent Insurance Agencies and Brokerages
+ References
No definition available.
+ Details**Name:**cinf_IndependentInsuranceAgenciesAndBrokerages**Namespace Prefix:**cinf_**Data Type:**xbrli:integerItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Number of Locations
+ References
No definition available.
+ Details**Name:**cinf_NumberOfLocations**Namespace Prefix:**cinf_**Data Type:**xbrli:integerItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Number of Subsidiaries
+ References
No definition available.
+ Details**Name:**cinf_NumberOfSubsidiaries**Namespace Prefix:**cinf_**Data Type:**xbrli:integerItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of earned premiums.
+ References
No definition available.
+ Details**Name:**cinf_PercentageOfPremiums**Namespace Prefix:**cinf_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Significant Accounting Policies [Line Items]
+ References
No definition available.
+ Details**Name:**cinf_SignificantAccountingPoliciesLineItems**Namespace Prefix:**cinf_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Unrealized gains on equity securities reclassified from accumulated other comprehensive income to retained earnings, after tax upon adoption of ASU 2016-01.
+ References
No definition available.
+ Details**Name:**cinf_UnrealizedgainsreclassifiedtoretainedearningsforASU201601aftertax**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2420-110228Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585
+ Details**Name:**us-gaap_AssetImpairmentCharges**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229
+ Details**Name:**us-gaap_Depreciation**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of estimated penalties recognized in the period arising from income tax examinations.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319
+ Details**Name:**us-gaap_IncomeTaxExaminationPenaltiesExpense**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The number of states the entity operates in as of the balance sheet date.
+ References
No definition available.
+ Details**Name:**us-gaap_NumberOfStatesInWhichEntityOperates**Namespace Prefix:**us-gaap_**Data Type:**xbrli:integerItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of investments classified as other.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.1(f,g)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910
+ Details**Name:**us-gaap_OtherInvestments**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.
+ References
No definition available.
+ Details**Name:**us-gaap_PropertyPlantAndEquipmentUsefulLife**Namespace Prefix:**us-gaap_**Data Type:**xbrli:durationItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.3(a)) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 325 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=75031664&loc=d3e22529-158502
+ Details**Name:**us-gaap_RealizedInvestmentGainsLosses**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value amount of the specified investment category of assets maintained in separate accounts as of the balance sheet date.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 55 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=6588021&loc=d3e7104-158389Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 80 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=6484115&loc=d3e19393-158473
+ Details**Name:**us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentFairValue**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901
+ Details**Name:**us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1**Namespace Prefix:**us-gaap_**Data Type:**xbrli:durationItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Weighted average remaining contractual term of exercisable stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901
+ Details**Name:**us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageRemainingContractualTerm2**Namespace Prefix:**us-gaap_**Data Type:**xbrli:durationItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of investments, not including unrealized gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, held at each balance sheet date and included in earnings for the period.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585
+ Details**Name:**us-gaap_UnrealizedGainLossOnInvestments**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_RangeAxis=us-gaap_MinimumMember**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_InvestmentTypeAxis=cinf_LifePolicyLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InvestmentTypeAxis=us-gaap_VentureCapitalFundsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InvestmentTypeAxis=us-gaap_RealEstateInvestmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementGeographicalAxis=cinf_StateMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementGeographicalAxis=stpr_OH**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementGeographicalAxis=cinf_OtherStateMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_MajorCustomersAxis=cinf_LargestCustomerMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_MajorCustomersAxis=cinf_AllOtherMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**cinf_ScheduleOfShareBasedCompensationArrangementByShareBasedPaymentAwardAxis=us-gaap_EmployeeStockOptionMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementBusinessSegmentsAxis=cinf_PropertyCasualtyInsuranceSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**invest_InvestmentSecuritiesClassAxis=us-gaap_EquitySecuritiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |