|**Property Casualty Loss and Loss Expenses (Tables)**         | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|------------------------------------------------------------- | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|**Premiums Written, Net, Property and Casualty [Abstract]**   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Consolidated Property Casualty Loss And Loss Expense Reserves | This table summarizes activity for our consolidated property casualty loss and loss expense reserves:(In millions)Three months ended March 31,20132012Gross loss and loss expense reserves, beginning of period$4,169$4,280Less reinsurance receivable356375Net loss and loss expense reserves, beginning of period3,8133,905Net incurred loss and loss expenses related to:Current accident year534655Prior accident years(10)(116)Total incurred524539Net paid loss and loss expenses related to:Current accident year121132Prior accident years392375Total paid513507Net loss and loss expense reserves, end of period3,8243,937Plus reinsurance receivable349352Gross loss and loss expense reserves, end of period$4,173$4,289
|                                                             
|                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|(In millions)                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Gross loss and loss expense reserves, beginning of period     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Less reinsurance receivable                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Net loss and loss expense reserves, beginning of period       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Net incurred loss and loss expenses related to:               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Current accident year                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Prior accident years                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Total incurred                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Net paid loss and loss expenses related to:                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Current accident year                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Prior accident years                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Total paid                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Net loss and loss expense reserves, end of period             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Plus reinsurance receivable                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Gross loss and loss expense reserves, end of period           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    

X- DefinitionConsolidated Property Casualty Loss And Loss Expense Reserves+ ReferencesNo definition available.+ Details**Name:**
                    cinf_ConsolidatedPropertyCasualtyLossAndLossExpenseReservesTableTextBlock**Namespace Prefix:**
                    cinf_**Data Type:**
                    nonnum:textBlockItemType**Balance Type:**
                    na**Period Type:**
                    duration X- Details**Name:**
                    us-gaap_PremiumsWrittenNetPropertyAndCasualtyAbstract**Namespace Prefix:**
                    us-gaap_**Data Type:**
                    xbrli:stringItemType**Balance Type:**
                    na**Period Type:**
                    duration