| **Deferred Policy Acquisition Costs (Deferred Policy Acquisition Costs And Asset Reconciliation Including The Amortized Deferred Policy Acquisition Costs) (Details) - USD ($) $ in Millions** | 12 Months Ended |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------|
||
| **Deferred Costs [Roll Forward]**                                                                                                                                                              |            |   |   |
| Deferred policy acquisition costs asset at January 1                                                                                                                                           | $ 905           | $ 805 | $ 774 |
| Capitalized deferred policy acquisition costs                                                                                                                                                  | 1,443           | 1,270 | 1,145 |
| Amortized deferred policy acquisition costs                                                                                                                                                    | (1,347)         | (1,197) | (1,106) |
| Shadow deferred policy acquisition costs                                                                                                                                                       | 13              | 27 | (8) |
| Deferred policy acquisition costs asset at December 31                                                                                                                                         | 1,014           | 905 | 805 |
| Life Insurance Segment                                                                                                                                                                         |            |   |   |
| **Deferred Costs [Roll Forward]**                                                                                                                                                              |            |   |   |
| Deferred policy acquisition costs asset at January 1                                                                                                                                           | 303             | 263 | 262 |
| Capitalized deferred policy acquisition costs                                                                                                                                                  | 60              | 59 | 58 |
| Amortized deferred policy acquisition costs                                                                                                                                                    | (44)            | (46) | (49) |
| Shadow deferred policy acquisition costs                                                                                                                                                       | 13              | 27 | (8) |
| Deferred policy acquisition costs asset at December 31                                                                                                                                         | 332             | 303 | 263 |
| Consolidated Property And Casualty Insurance Entity                                                                                                                                            |            |   |   |
| **Deferred Costs [Roll Forward]**                                                                                                                                                              |            |   |   |
| Deferred policy acquisition costs asset at January 1                                                                                                                                           | 602             | 542 | 512 |
| Capitalized deferred policy acquisition costs                                                                                                                                                  | 1,383           | 1,211 | 1,087 |
| Amortized deferred policy acquisition costs                                                                                                                                                    | (1,303)         | (1,151) | (1,057) |
| Deferred policy acquisition costs asset at December 31                                                                                                                                         | $ 682           | $ 602 | $ 542 |

| X                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Deferred Costs
+ References
No definition available.
+ Details**Name:**cinf_DeferredCostsRollForward**Namespace Prefix:**cinf_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of amortization expense (reversal of expense) for deferred policy acquisition costs.
+ References
Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 30 -Section 55 -Paragraph 2 -URI https://asc.fasb.org/extlink&oid=124504731&loc=d3e11522-158419Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 45 -Paragraph 2 -Subparagraph (d) -URI https://asc.fasb.org/extlink&oid=6480726&loc=d3e6691-158385Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (g)(1) -URI https://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(7)(a)) -URI https://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 30 -Section 50 -Paragraph 2B -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=124505477&loc=SL117422543-158416Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (c) -URI https://asc.fasb.org/extlink&oid=35755530&loc=d3e11264-158415
+ Details**Name:**us-gaap_DeferredPolicyAcquisitionCostAmortizationExpense**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of other increase (decrease) to amortization expense of deferred policy acquisition cost (DAC).
+ References
No definition available.
+ Details**Name:**us-gaap_DeferredPolicyAcquisitionCostAmortizationExpenseOther**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of deferred policy acquisition cost capitalized on contract remaining in force.
+ References
Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 30 -Section 50 -Paragraph 2B -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=124505477&loc=SL117422543-158416Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 30 -Section 50 -Paragraph 2B -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=124505477&loc=SL117422543-158416Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 825 -Section 45 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=124506110&loc=d3e32546-158582Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (g)(1) -URI https://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(7)) -URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910Reference 6: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 30 -Section 55 -Paragraph 2 -URI https://asc.fasb.org/extlink&oid=124504731&loc=d3e11522-158419
+ Details**Name:**us-gaap_DeferredPolicyAcquisitionCosts**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of deferred policy acquisition cost capitalized.
+ References
Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 30 -Section 50 -Paragraph 2B -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=124505477&loc=SL117422543-158416Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (g)(1) -URI https://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 30 -Section 55 -Paragraph 2 -URI https://asc.fasb.org/extlink&oid=124504731&loc=d3e11522-158419
+ Details**Name:**us-gaap_DeferredPolicyAcquisitionCostsAdditions**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementBusinessSegmentsAxis=cinf_LifeInsuranceMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementBusinessSegmentsAxis=cinf_ConsolidatedPropertyAndCasualtyInsuranceMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |