| **Fair Value Measurements - Fair Value of Life Policy Loans, Deferred Annuities, and Structured Settlements (Detail) - USD ($) $ in Millions** | Mar. 31, 2022 | Dec. 31, 2021 |
|------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis**                                                            |          |          |
| Fair value of life policy loans                                                                                                                | $ 40          | $ 44          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 881           | 979           |
| Quoted prices in active markets for identical assets (Level 1)                                                   |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis**                                                            |          |          |
| Fair value of life policy loans                                                                                                                | 0             | 0             |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 0             | 0             |
| Significant other observable inputs (Level 2)                                                                                   |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis**                                                            |          |          |
| Fair value of life policy loans                                                                                                                | 0             | 0             |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 177           | 201           |
| Significant unobservable inputs (Level 3)                                                                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis**                                                            |          |          |
| Fair value of life policy loans                                                                                                                | 40            | 44            |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 704           | 778           |
| Deferred annuities                                                                                                                             |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis**                                                            |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 704           | 778           |
| Deferred annuities | Quoted prices in active markets for identical assets (Level 1)                              |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis**                                                            |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 0             | 0             |
| Deferred annuities | Significant other observable inputs (Level 2)                                                              |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis**                                                            |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 0             | 0             |
| Deferred annuities | Significant unobservable inputs (Level 3)                                                                            |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis**                                                            |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 704           | 778           |
| Structured settlements                                                                                                                         |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis**                                                            |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 177           | 201           |
| Structured settlements | Quoted prices in active markets for identical assets (Level 1)                          |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis**                                                            |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 0             | 0             |
| Structured settlements | Significant other observable inputs (Level 2)                                                          |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis**                                                            |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 177           | 201           |
| Structured settlements | Significant unobservable inputs (Level 3)                                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis**                                                            |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | $ 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
No definition available.
+ Details**Name:**us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value portion of liability related to investment contracts for example, but not limited to, guaranteed investment contract or annuities.
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 825 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6487514&loc=d3e32427-158581
+ Details**Name:**us-gaap_LiabilitiesRelatedToInvestmentContractsFairValueDisclosure**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -URI http://asc.fasb.org/subtopic&trid=2196772
+ Details**Name:**us-gaap_LoansReceivableFairValueDisclosure**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DerivativeInstrumentRiskAxis=cinf_DeferredAnnuitiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DerivativeInstrumentRiskAxis=us-gaap_StructuredFinanceMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |