|**Income Taxes**                       | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
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|**Income Tax Disclosure [Abstract]**   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Income Taxes                           | Income TaxesThe differences between the 21% statutory federal income tax rate and our effective income tax rate were as follows:(Dollars in millions)Three months ended September 30,Nine months ended September 30,2023202220232022Tax at statutory rate:$(31)21.0%$(122)21.0%$16521.0%$(416)21.0%Increase (decrease) resulting from:Tax-exempt income from municipal bonds(5)3.4(5)0.9(15)(1.9)(15)0.8Dividend received exclusion(5)3.4(5)0.9(16)(2.0)(15)0.8Release of unrecognized tax benefit——(34)5.9——(34)1.7Other(8)5.35(0.8)(8)(1.1)(1)—Provision (benefit) for income taxes$(49)33.1%$(161)27.9%$12616.0%$(481)24.3%The provision (benefit) for federal income taxes is based upon filing a consolidated income tax return for the company and its domestic subsidiaries.We continue to believe that after considering all positive and negative evidence of taxable income in the carryback and carryforward periods as permitted by law, it is more likely than not that all of the deferred tax assets on our U.S. domestic operations will be realized. As a result, we have no valuation allowance for our U.S. domestic operations at September 30, 2023, and December 31, 2022. As more fully discussed below, we do carry a valuation allowance on the deferred tax assets related to Cincinnati Global Underwriting Ltd.SM(Cincinnati Global).Unrecognized Tax BenefitsDuring the third quarter of 2022, we received favorable guidance from the Internal Revenue Service (IRS) supporting our tax position related to our unrecognized tax benefit set up in 2018. As a result of this guidance, we released our $34 million gross unrecognized tax benefit liability at September 30, 2022. The $34 million release was recognized as an additional income tax benefit and shown separately in our effective income tax rate reconciliation.Cincinnati GlobalAs a result of operations for the three and nine months ended September 30, 2023, Cincinnati Global decreased its net deferred tax assets by $10 million and $20 million, respectively,with an offsetting decrease of $10 million and $20 million, respectively, to the valuation allowance. Cincinnati Global had a net deferred tax asset of $11 million and an offsetting valuation allowance of $11 million at September 30, 2023.Deferred tax assets are reduced by a valuation allowance when management believes it is more likely than not that some, or all, of the deferred tax assets will not be realized. After considering all positive and negative evidence, we continue to believe it is appropriate to carry a valuation allowance at September 30, 2023.Cincinnati Global had operating loss carryforwards in the United States of $6 million and $5 million and in the United Kingdom of $99 million and $109 million at September 30, 2023, and December 31, 2022, respectively. These Cincinnati Global losses can only be utilized within the Cincinnati Global group.
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|(Dollars in millions)                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
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|Tax at statutory rate:                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Increase (decrease) resulting from:    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Tax-exempt income from municipal bonds |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Dividend received exclusion            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
|Release of unrecognized tax benefit    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
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|Provision (benefit) for income taxes   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
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X- ReferencesNo definition available.
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