| **Reinsurance (Incurred Consolidated Property Casualty Insurance Loss And Loss Expenses On Assumed And Ceded Business) (Details) (USD $)In Millions, unless otherwise specified** | 12 Months Ended                                                                                                                                                        |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| Net incurred loss and loss expenses                                                                                                                                               | $ 2,856us-gaap_PolicyholderBenefitsAndClaimsIncurredNet                                                                                                                | $ 2,505us-gaap_PolicyholderBenefitsAndClaimsIncurredNet | $ 2,322us-gaap_PolicyholderBenefitsAndClaimsIncurredNet |
| Property, Liability and Casualty Insurance Product Line [Member]                                                                                                                  |                                                                                                                                                                   |   |   |
| Direct incurred loss and loss expenses                                                                                                                                            | 2,661us-gaap_PolicyholderBenefitsAndClaimsIncurredGross/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember             | 2,323us-gaap_PolicyholderBenefitsAndClaimsIncurredGross/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember | 2,235us-gaap_PolicyholderBenefitsAndClaimsIncurredGross/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember |
| Assumed incurred loss and loss expenses                                                                                                                                           | 6us-gaap_ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountAssumed/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember  | 11us-gaap_ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountAssumed/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember | 6us-gaap_ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountAssumed/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember |
| Ceded incurred loss and loss expenses                                                                                                                                             | (40)cinf_ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCededNet/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember | (33)cinf_ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCededNet/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember | (104)cinf_ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCededNet/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember |
| Net incurred loss and loss expenses                                                                                                                                               | $ 2,627us-gaap_PolicyholderBenefitsAndClaimsIncurredNet/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember             | $ 2,301us-gaap_PolicyholderBenefitsAndClaimsIncurredNet/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember | $ 2,137us-gaap_PolicyholderBenefitsAndClaimsIncurredNet/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember |

| X                                                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Reinsurance Effect on Claims and Benefits Incurred, Amount Ceded, Net
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, before effect of policies assumed or ceded, of expense related to provision for policy benefits and costs incurred.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.5) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 5 -Article 7
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after effects of policies assumed or ceded, of expense related to the provision for policy benefits and costs incurred.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.5) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 5 -Article 7Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6811-158387
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of policy benefits and costs incurred for policies assumed.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6811-158387
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| X                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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