| **Property Casualty Loss And Loss Expenses (Narrative) (Details) (USD $)**              | 12 Months Ended |
|-----------------------------------------------------------------------------------------|-----------------|
||
| **Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]** |            |   |   |
| Favorable reserve development on prior accident years                                   | $ 147,000,000   | $ 396,000,000 | $ 285,000,000 |
| Net loss and loss expense reserves for asbestos and environmental claims                | 77,000,000      | 67,000,000 |   |
| Environmental claims related to mold                                                    | 51,000,000      | 54,000,000 |   |
| Percentage of reserves for asbestos and environmental claims                            | 1.90%           | 1.80% |   |
| Maximum [Member]                                                                        |            |   |   |
| **Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]** |            |   |   |
| Reinsurance retention                                                                   | 500,000         |   |   |
| Life and Health Loss Reserves [Member]                                                  |            |   |   |
| **Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]** |            |   |   |
| Reserve for loss and loss expenses                                                      | 70,000,000      | 61,000,000 | 59,000,000 |
| Homeowner [Member]                                                                      |            |   |   |
| **Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]** |            |   |   |
| Favorable reserve development on prior accident years                                   | 19,000,000      | 52,000,000 |   |
| Commercial Lines [Member]                                                               |            |   |   |
| **Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]** |            |   |   |
| Favorable reserve development on prior accident years                                   | 95,000,000      | 292,000,000 | 234,000,000 |
| Increase in favorable reserve developement on prior accident                            | 249,000,000     | 111,000,000 |   |
| Commercial Lines [Member] | Workers' Compensation [Member]                              |            |   |   |
| **Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]** |            |   |   |
| Favorable reserve development on prior accident years                                   | 14,000,000      | 74,000,000 | 97,000,000 |
| Commercial Lines [Member] | Catastrophe Development [Member]                            |            |   |   |
| **Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]** |            |   |   |
| Favorable reserve development on prior accident years                                   |            | 39,000,000 |   |
| Commercial Lines [Member] | Commerical Casualty Business [Member]                       |            |   |   |
| **Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]** |            |   |   |
| Favorable reserve development on prior accident years                                   | 70,000,000      | 177,000,000 | 132,000,000 |
| Commercial Lines [Member] | Commercial Property Segment [Member]                        |            |   |   |
| **Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]** |            |   |   |
| Favorable reserve development on prior accident years                                   | $ 22,000,000    |   |   |

| X                                                                                                                                                                                                                                                                                    |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Asbestos and environmental reinsurance retention.
+ References
No definition available.
+ Details**Name:**cinf_AsbestosAndEnvironmentalReinsuranceRetention**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Increase in the recovery of liability for unpaid claims and claims adjustment expense, incurred claims, prior years.
+ References
No definition available.
+ Details**Name:**cinf_IncreaseInRecoveryOfLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsPriorYears**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Carrying amount as of the balance sheet date of reserves for the costs of settling insured claims and costs incurred in the claims settlement process attributable to environmental claims related to mold.
+ References
No definition available.
+ Details**Name:**cinf_LiabilityForAsbestosAndEnvironmentalClaimsMold**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of reserves for asbestos and environmental claims to total loss and loss expense reserves.
+ References
No definition available.
+ Details**Name:**cinf_PercentageOfReservesForAsbestosAndEnvironmentalClaims**Namespace Prefix:**cinf_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Recovery of Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims, Prior Years
+ References
No definition available.
+ Details**Name:**cinf_RecoveryOfLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsPriorYears**Namespace Prefix:**cinf_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Carrying amount as of the balance sheet date of reserves for the costs of settling insured claims and costs incurred in the claims settlement process attributable to asbestos and environmental claims, net of estimated reinsurance recoveries.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437
+ Details**Name:**us-gaap_LiabilityForAsbestosAndEnvironmentalClaimsNet**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a),(b),(c) -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437
+ Details**Name:**us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |