| **Life Policy And Investment Contract Reservess (Reserve In Addition To The Account Balance Based On Expected No-Lapse Guarantee Benefits And Expected Policy Assessments) (Details) (USD $)In Millions, unless otherwise specified** | Dec. 31, 2014                                                                                                                                                     | Dec. 31, 2013                                                                                                                                                     |
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| **Liability for Future Policy Benefit, by Product Segment**                                                                                                                                                                           |                                                                                                                                                              |                                                                                                                                                              |
| Life policy and investment contract reserves                                                                                                                                                                                          | $ 2,497us-gaap_LiabilityForFuturePolicyBenefitsLife                                                                                                               | $ 2,390us-gaap_LiabilityForFuturePolicyBenefitsLife                                                                                                               |
| Ordinary/Traditional Life                                                                                                                                                                                                             |                                                                                                                                                              |                                                                                                                                                              |
| **Liability for Future Policy Benefit, by Product Segment**                                                                                                                                                                           |                                                                                                                                                              |                                                                                                                                                              |
| Life policy and investment contract reserves                                                                                                                                                                                          | 875us-gaap_LiabilityForFuturePolicyBenefitsLife/ us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis= cinf_IndividualOrdinaryLifeInsuranceMember | 815us-gaap_LiabilityForFuturePolicyBenefitsLife/ us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis= cinf_IndividualOrdinaryLifeInsuranceMember |
| Deferred Annuities                                                                                                                                                                                                                    |                                                                                                                                                              |                                                                                                                                                              |
| **Liability for Future Policy Benefit, by Product Segment**                                                                                                                                                                           |                                                                                                                                                              |                                                                                                                                                              |
| Life policy and investment contract reserves                                                                                                                                                                                          | 863us-gaap_LiabilityForFuturePolicyBenefitsLife/ us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis= cinf_DeferredAnnuitiesMember               | 862us-gaap_LiabilityForFuturePolicyBenefitsLife/ us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis= cinf_DeferredAnnuitiesMember               |
| Universal Life                                                                                                                                                                                                                        |                                                                                                                                                              |                                                                                                                                                              |
| **Liability for Future Policy Benefit, by Product Segment**                                                                                                                                                                           |                                                                                                                                                              |                                                                                                                                                              |
| Life policy and investment contract reserves                                                                                                                                                                                          | 530us-gaap_LiabilityForFuturePolicyBenefitsLife/ us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis= us-gaap_UniversalLifeMember                | 508us-gaap_LiabilityForFuturePolicyBenefitsLife/ us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis= us-gaap_UniversalLifeMember                |
| Structured Settlements                                                                                                                                                                                                                |                                                                                                                                                              |                                                                                                                                                              |
| **Liability for Future Policy Benefit, by Product Segment**                                                                                                                                                                           |                                                                                                                                                              |                                                                                                                                                              |
| Life policy and investment contract reserves                                                                                                                                                                                          | 182us-gaap_LiabilityForFuturePolicyBenefitsLife/ us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis= cinf_StructuredSettlementsMember           | 189us-gaap_LiabilityForFuturePolicyBenefitsLife/ us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis= cinf_StructuredSettlementsMember           |
| Other                                                                                                                                                                                                                                 |                                                                                                                                                              |                                                                                                                                                              |
| **Liability for Future Policy Benefit, by Product Segment**                                                                                                                                                                           |                                                                                                                                                              |                                                                                                                                                              |
| Life policy and investment contract reserves                                                                                                                                                                                          | $ 47us-gaap_LiabilityForFuturePolicyBenefitsLife/ us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis= cinf_OtherLifeMember                      | $ 16us-gaap_LiabilityForFuturePolicyBenefitsLife/ us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis= cinf_OtherLifeMember                      |

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| - Definition
Amount of accrued obligation to policyholders that relates to insured events under long-term life insurance contracts.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 25 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=28366191&loc=d3e13145-158430Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 13 -Subparagraph a -Article 7Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.13(a)(1)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910
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| - Details**Name:**us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis=cinf_IndividualOrdinaryLifeInsuranceMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
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| - Details**Name:**us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis=cinf_OtherLifeMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
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| X                                                                                                                                                                                        |
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| - Details**Name:**us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis=us-gaap_UniversalLifeMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |