| **Account Values by Range of Guaranteed Minimum Crediting Rates (Details) - Investment contract reserves: - USD ($) $ in Millions**                                                                                    | Sep. 30, 2024 | Jun. 30, 2024 | Dec. 31, 2023 | Sep. 30, 2023 | Jun. 30, 2023 |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|---------------|---------------|
| Deferred Fixed Annuity                                                                                                                                                                                                 |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | $ 605         | $ 618         | $ 656         | $ 680         | $ 696         |
| Deferred Fixed Annuity | Policyholder Account Balance, at Guaranteed Minimum Crediting Rate                                                                                                                            |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 51            |          |          | 55            |          |
| Deferred Fixed Annuity | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0001 to 0050                                                                                                |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 309           |          |          | 380           |          |
| Deferred Fixed Annuity | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0051 to 0150                                                                                                |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 14            |          |          | 16            |          |
| Deferred Fixed Annuity | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0151 and Greater                                                                                            |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 231           |          |          | 229           |          |
| Deferred Fixed Annuity | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0200 to 0299                                                                                                      |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 558           |          |          | 630           |          |
| Deferred Fixed Annuity | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0200 to 0299 | Policyholder Account Balance, at Guaranteed Minimum Crediting Rate                                 |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 4             |          |          | 5             |          |
| Deferred Fixed Annuity | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0200 to 0299 | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0001 to 0050     |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 309           |          |          | 380           |          |
| Deferred Fixed Annuity | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0200 to 0299 | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0051 to 0150     |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 14            |          |          | 16            |          |
| Deferred Fixed Annuity | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0200 to 0299 | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0151 and Greater |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 231           |          |          | 229           |          |
| Deferred Fixed Annuity | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0300 to 0399                                                                                                      |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 47            |          |          | 50            |          |
| Deferred Fixed Annuity | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0300 to 0399 | Policyholder Account Balance, at Guaranteed Minimum Crediting Rate                                 |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 47            |          |          | 50            |          |
| Deferred Fixed Annuity | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0300 to 0399 | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0001 to 0050     |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 0             |          |          | 0             |          |
| Deferred Fixed Annuity | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0300 to 0399 | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0051 to 0150     |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 0             |          |          | 0             |          |
| Deferred Fixed Annuity | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0300 to 0399 | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0151 and Greater |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 0             |          |          | 0             |          |
| Universal life                                                                                                                                                                                                         |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 456           | $ 456         | $ 457         | 456           | $ 456         |
| Universal life | Policyholder Account Balance, at Guaranteed Minimum Crediting Rate                                                                                                                                    |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 328           |          |          | 396           |          |
| Universal life | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0001 to 0050                                                                                                        |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 55            |          |          | 0             |          |
| Universal life | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0051 to 0150                                                                                                        |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 68            |          |          | 57            |          |
| Universal life | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0151 and Greater                                                                                                    |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 5             |          |          | 3             |          |
| Universal life | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0200 to 0299                                                                                                              |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 124           |          |          | 120           |          |
| Universal life | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0200 to 0299 | Policyholder Account Balance, at Guaranteed Minimum Crediting Rate                                         |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 0             |          |          | 60            |          |
| Universal life | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0200 to 0299 | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0001 to 0050             |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 55            |          |          | 0             |          |
| Universal life | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0200 to 0299 | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0051 to 0150             |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 64            |          |          | 57            |          |
| Universal life | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0200 to 0299 | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0151 and Greater         |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 5             |          |          | 3             |          |
| Universal life | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0300 to 0399                                                                                                              |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 54            |          |          | 54            |          |
| Universal life | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0300 to 0399 | Policyholder Account Balance, at Guaranteed Minimum Crediting Rate                                         |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 50            |          |          | 54            |          |
| Universal life | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0300 to 0399 | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0001 to 0050             |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 0             |          |          | 0             |          |
| Universal life | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0300 to 0399 | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0051 to 0150             |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 4             |          |          | 0             |          |
| Universal life | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0300 to 0399 | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0151 and Greater         |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 0             |          |          | 0             |          |
| Universal life | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0400 and Greater                                                                                                          |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 278           |          |          | 282           |          |
| Universal life | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0400 and Greater | Policyholder Account Balance, at Guaranteed Minimum Crediting Rate                                     |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 278           |          |          | 282           |          |
| Universal life | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0400 and Greater | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0001 to 0050         |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 0             |          |          | 0             |          |
| Universal life | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0400 and Greater | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0051 to 0150         |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | 0             |          |          | 0             |          |
| Universal life | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range from 0400 and Greater | Policyholder Account Balance, above Guaranteed Minimum Crediting Rate, Range from 0151 and Greater     |          |          |          |          |          |
| **Policyholder Account Balance, Guaranteed Minimum Crediting Rate [Line Items]**                                                                                                                                       |          |          |          |          |          |
| Balance, end of period                                                                                                                                                                                                 | $ 0           |          |          | $ 0           |          |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 55 -Paragraph 29F -Publisher FASB -URI https://asc.fasb.org/1943274/2147480046/944-40-55-29FReference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 7A -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-7A
+ Details**Name:**us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount due to policyholder. Includes, but is not limited to, unpaid policy dividend, retrospective refund, and undistributed earnings on participating business. Excludes future policy benefit and claim expense.
+ References
Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 7A -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-7AReference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 7A -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-7AReference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(14)(a)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1Reference 4: http://www.xbrl.org/2003/role/exampleRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 55 -Paragraph 29F -Publisher FASB -URI https://asc.fasb.org/1943274/2147480046/944-40-55-29FReference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 7A -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-7A
+ Details**Name:**us-gaap_PolicyholderFunds**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**srt_ProductOrServiceAxis=us-gaap_DeferredFixedAnnuityMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_EquitySecuritiesByIndustryAxis=cinf_InvestmentcontractreservesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateAxis=us-gaap_PolicyholderAccountBalanceAtGuaranteedMinimumCreditingRateMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateAxis=us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateRangeFrom0001To0050Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateAxis=us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateRangeFrom0051To0150Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateAxis=us-gaap_PolicyholderAccountBalanceAboveGuaranteedMinimumCreditingRateRangeFrom0151AndGreaterMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeAxis=us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0200To0299Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeAxis=us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0300To0399Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**srt_ProductOrServiceAxis=us-gaap_UniversalLifeMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeAxis=us-gaap_PolicyholderAccountBalanceGuaranteedMinimumCreditingRateRangeFrom0400AndGreaterMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |