|**Life Policy and Investment Contract Reserves (Tables)**      | 3 Months Ended                                                                                                                                                                                                                                                                                     
|-------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|**Liability for Future Policy Benefits [Abstract]**            |                                                                                                                                                                                                                                                                                                    
|Reserve For Losses Loss Adjustment Expenses Table [Text Block] | This table summarizes our life policy and investment contract reserves:(In millions)March 31, 2013December 31, 2012Ordinary/traditional life$760$752Universal life487483Deferred annuities852850Structured settlements194193Other1717Total life policy and investment contract reserves$2,310$2,295
|                                                              
|                                                               |                                                                                                                                                                                                                                                                                                    
|(In millions)                                                  |                                                                                                                                                                                                                                                                                                    
|Ordinary/traditional life                                      |                                                                                                                                                                                                                                                                                                    
|Universal life                                                 |                                                                                                                                                                                                                                                                                                    
|Deferred annuities                                             |                                                                                                                                                                                                                                                                                                    
|Structured settlements                                         |                                                                                                                                                                                                                                                                                                    
|Other                                                          |                                                                                                                                                                                                                                                                                                    
|Total life policy and investment contract reserves             |                                                                                                                                                                                                                                                                                                    

X- DefinitionReserve for Losses Loss Adjustment Expenses [Table Text Block]+ ReferencesNo definition available.+ Details**Name:**
                    cinf_ReserveForLossesLossAdjustmentExpensesTableTextBlock**Namespace Prefix:**
                    cinf_**Data Type:**
                    nonnum:textBlockItemType**Balance Type:**
                    na**Period Type:**
                    duration X- Details**Name:**
                    us-gaap_LiabilityForFuturePolicyBenefitsAbstract**Namespace Prefix:**
                    us-gaap_**Data Type:**
                    xbrli:stringItemType**Balance Type:**
                    na**Period Type:**
                    duration