|**Life Policy And Investment Contract Reserves (Tables)**                                                                 | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                     
|------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
|**Liability for Future Policy Benefit, before Reinsurance [Abstract]**                                                    |                                                                                                                                                                                                                                                                                                                                                                                                     
|Reserve In Addition To The Account Balance, Based on Expected No-Lapse Guarantee Benefits And Expected Policy Assessments | This table summarizes our life policy and investment contract reserves:(Dollars in millions)At December 31,20192018Life policy reserves:Ordinary/traditional life$1,226$1,149Other5048Subtotal1,2761,197Investment contract reserves:Deferred annuities760787Universal life640632Structured settlements151156Other87Subtotal1,5591,582Total life policy and investment contract reserves$2,835$2,779
|                                                                                                                         
|                                                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                     
|(Dollars in millions)                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                     
|Life policy reserves:                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                     
|Ordinary/traditional life                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                     
|Other                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                     
|Subtotal                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                     
|Investment contract reserves:                                                                                             |                                                                                                                                                                                                                                                                                                                                                                                                     
|Deferred annuities                                                                                                        |                                                                                                                                                                                                                                                                                                                                                                                                     
|Universal life                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                     
|Structured settlements                                                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                     
|Other                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                     
|Subtotal                                                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                     
|Total life policy and investment contract reserves                                                                        |                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                     

X- DefinitionReserve For Losses And Loss Adjustment Expenses
+ ReferencesNo definition available.
+ Details**Name:**
cinf_ReserveForLossesLossAdjustmentExpensesTextBlock**Namespace Prefix:**
cinf_**Data Type:**
nonnum:textBlockItemType**Balance Type:**
na**Period Type:**
duration X- ReferencesNo definition available.
+ Details**Name:**
us-gaap_LiabilityForFuturePolicyBenefitsAbstract**Namespace Prefix:**
us-gaap_**Data Type:**
xbrli:stringItemType**Balance Type:**
na**Period Type:**
duration