| **Accounting Policies**            | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Accounting Policies [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
| Accounting Policies                | Accounting PoliciesThe condensed consolidated financial statements include the accounts of Cincinnati Financial Corporation and its consolidated subsidiaries, each of which is wholly owned. These statements are presented in conformity with accounting principles generally accepted in the United States of America (GAAP). All intercompany balances and transactions have been eliminated in consolidation. The preparation of financial statements in conformity with GAAP requires us to make estimates and assumptions that affect amounts reported in the financial statements and accompanying notes. Our actual results could differ from those estimates. Certain financial information that is normally included in annual financial statements prepared in accordance with GAAP, but that is not required for interim reporting purposes, has been condensed or omitted. Our March 31, 2020, condensed consolidated financial statements are unaudited. We believe that we have made all adjustments, consisting only of normal recurring accruals, that are necessary for fair presentation. These condensed consolidated financial statements should be read in conjunction with our consolidated financial statements included in our 2019 Annual Report on Form 10-K. The results of operations for interim periods do not necessarily indicate results to be expected for the full year.The World Health Organization declared the 2019 novel coronavirus (SARS-CoV-2 or COVID-19) outbreak a Public Health Emergency of International Concern on January 30, 2020, and a pandemic on March 11, 2020. The pandemic outbreak has caused an economic downturn on a global scale, including temporary closures of many businesses and reduced consumer spending due to shelter-in-place and other governmental regulations, as well as significant market disruption and volatility. The company continues to monitor the impact of the pandemic as it unfolds. The company cannot, at this time, predict the impact the pandemic will have on its future consolidated financial position, cash flows or results of operations, however the impact could be material. The company's future financial results and operations depends in part on the duration and severity of the pandemic and what actions are taken to mitigate the outbreak.Adopted Accounting UpdatesASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial InstrumentsIn June 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, as well as additional implementation related ASU's in 2018, 2019 and 2020. These ASU’s amend previous guidance on the impairment of financial instruments by adding an impairment model that allows an entity to recognize expected credit losses as an allowance rather than impairing as they are incurred. The new guidance is intended to reduce complexity of credit impairment models and result in a more timely recognition of expected credit losses. The standards require the company to consider all relevant information at the time of estimating the expected credit loss, including past events, the current environment, and reasonable and supportable forecasts over the life of the asset.These ASU's also eliminated the other-than-temporary impairment model for available for sale fixed-maturity securities by requiring that credit related impairments be recognized through an allowance account. Changes in the allowance account are recorded in the period of change as a credit loss expense or reversal of credit loss expense. The measurement of credit losses is not impacted, except that credit losses recognized are limited to the amount by which fair value is below amortized cost and that the length of time that a security has been below amortized cost cannot be considered. These ASU's retain the guidance requiring that impaired securities intended to be sold have their amortized cost basis written down to fair value through net income. The company adopted these ASU's on January 1, 2020 and applied them on a modified retrospective basis. As a result of this adoption, an after-tax cumulative effect decrease of $2 million was made to retained earnings representing an increase to the overall valuation allowances for financial instruments measured at amortized cost. These ASU's will be applied to available for sale fixed-maturity securities prospectively with no adjustments to the amortized cost basis of securities for which an other-than-temporary impairment had been previously recognized. The company has elected not to measure expected credit losses for accrued interest receivables related to its finance receivables and fixed-maturity securities. Pending Accounting UpdatesASU 2018-12, Financial Services - Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration ContractsIn August 2018, the FASB issued ASU 2018-12, Financial Services - Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration Contracts. ASU 2018-12 is intended to improve the timeliness of recognizing changes in the liability for future policy benefits and modify the rate used to discount future cash flows. The ASU will simplify and improve the accounting for certain market-based options or guarantees associated with deposit or account balance contracts, simplify amortization of deferred acquisition costs while improving and expanding required disclosures. In November 2019, the FASB issued ASU 2019-09, Financial Services - Insurance (Topic 944): Effective Date. ASU 2019-09 delays the effective date of ASU 2018-12 by one year to interim and annual reporting periods beginning after December 15, 2021. These ASU's have not yet been adopted. Management is currently evaluating the impact on our company's consolidated financial position, cash flows and results of operations. |

| X                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - References
No definition available.
+ Details**Name:**us-gaap_AccountingPoliciesAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The entire disclosure for all significant accounting policies of the reporting entity.
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -URI http://asc.fasb.org/topic&trid=2122369
+ Details**Name:**us-gaap_SignificantAccountingPoliciesTextBlock**Namespace Prefix:**us-gaap_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |