| **Accounting Policies**            | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    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| **Accounting Policies [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             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| 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). Effective February 28, 2019, the company acquired MSP Underwriting Limited, a London-based, global specialty underwriter. MSP was rebranded as Cincinnati Global Underwriting Ltd.SM (Cincinnati Global) effective May 1, 2019, reflecting its new identity as a subsidiary of the corporation. Refer to Note 14, Acquisition, for additional information. The interim condensed consolidated financial statements include Cincinnati Global's results for the period from February 28, 2019, through June 30, 2019. Foreign exchange rates related to Cincinnati Global's operations did not have a material impact to our condensed consolidated financial statements. 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 June 30, 2019, 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 2018 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.Adopted Accounting UpdatesASU 2016-02, Leases (Topic 842)In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-02, Leases(Topic 842). The main provision of ASU 2016-02 requires the recognition of lease assets and lease liabilities by lessees for those leases classified as operating leases under previous GAAP. The effective date of ASU 2016-02 is for interim and annual reporting periods beginning after December 15, 2018. In July 2018, the FASB issued ASU 2018-10, Codification Improvements to Topic 842 and ASU 2018-11, Targeted Improvements to Topic 842. ASU 2018-10 makes narrow-scope amendments to certain aspects of the new leasing standard while ASU 2018-11 provides relief from costs of implementing certain aspects of the new leasing standard. The company adopted this ASU effective January 1, 2019, and it did not have a material impact on our company's consolidated financial position, cash flows or results of operations. As of June 30, 2019, this ASU resulted in recognizing a right-of-use asset and lease liability each for $15 million recorded in other assets and long-term debt and lease obligations line items, respectively, on our condensed consolidated balance sheets. The company has elected the practical expedient package for carrying forward historical lease classifications, not re-evaluating for embedded leases and not reassessing initial direct costs. The company also elected additional practical expedients to not recognize short-term leases on the balance sheet and to only combine lease and nonlease components for certain asset classes. We also elected not to restate prior periods. In support of our insurance operations, the company leases real estate properties which qualify as operating leases and also leases equipment and autos which qualify as finance leases. The lease term for real estate properties is typically five years while the term for equipment and autos is three to six years. ASU 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt SecuritiesIn March 2017, the FASB issued ASU 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities. ASU 2017-08 amends guidance on the amortization period of premiums on certain purchased callable debt securities. The amendments shorten the amortization period of premiums on certain purchased callable debt securities to the earliest call date. The amendments should be applied on a modified retrospective basis through a cumulative-effect adjustment to beginning retained earnings. The effective date of ASU 2017-08 is for interim and annual reporting periods beginning after December 15, 2018. The company adopted this ASU effective January 1, 2019, and it did not have a material impact on our company's consolidated financial position, cash flows or results of operations.ASU 2018-07, Compensation - Stock Compensation (Topic 718) - Improvements to Nonemployee Share-Based Payment AccountingIn June 2018, the FASB issued ASU 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting. ASU 2018-07 expands the scope of Topic 718, Compensation - Stock Compensation, which currently only includes share-based payments issued to employees, to include share-based payments issued to nonemployees for the acquisition of goods and services. The effective date of ASU 2018-07 is for interim and annual reporting periods beginning after December 15, 2018. The company adopted this ASU effective January 1, 2019, and it did not have a material impact on our company's consolidated financial position, cash flows or results of operations.Pending Accounting UpdatesASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial InstrumentsIn June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. In addition, through June 2019, the FASB issued ASU 2018-19, Codification Improvements to Topic 326, ASU 2019-04, Codification Improvements to Topic 326 and ASU 2019-05, Targeted Transition Relief. 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 guidance is effective for reporting periods beginning after December 15, 2019, and for most affected instruments must be adopted using a modified retrospective approach, with a cumulative effect adjustment recorded to beginning retained earnings. These ASU's have not yet been adopted; however, they are not expected to have a material impact on our company's consolidated financial position, cash flows or results of operations.ASU 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment In January 2017, the FASB issued ASU 2017-04, Intangibles - Goodwill and Other (Topic 350) - Simplifying the Test for Goodwill Impairment. ASU 2017-04 simplifies the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. Instead, an entity should perform its goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value. The loss recognized should not exceed the total amount of goodwill allocated to that reporting unit and income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit should be considered. The effective date of ASU 2017-04 is for interim and annual goodwill impairment tests performed in any fiscal years beginning after December 15, 2019. The ASU has not yet been adopted; however, it is not expected to have a material impact on our company's consolidated financial position, cash flows or results of operations.ASU 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. The effective date of ASU 2018-12 is for interim and annual reporting periods beginning after December 15, 2020. The ASU has not yet been adopted. Management is currently evaluating the impact on our company's consolidated financial position, cash flows and results of operations.ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value MeasurementIn August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement. ASU 2018-13 clarifies the fair value measurement disclosure requirements of ASC 820 by adding, eliminating and modifying disclosures. The effective date of ASU 2018-13 is for interim and annual reporting periods beginning after December 15, 2019. The ASU has not yet been adopted; however, it is not expected to have a material impact on our company's consolidated financial position, cash flows or results of operations.ASU 2018-14, Compensation - Retirement Benefits - Defined Benefit Plans - General (Topic 715-20): Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit PlansIn August 2018, the FASB issued ASU 2018-14, Compensation - Retirement Benefits - Defined Benefit Plans - General (Topic 715-20): Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans. ASU 2018-14 clarifies the guidance in ASC 715 to add, remove, and clarify disclosure requirements related to defined benefit pension and other postretirement plans. The effective date of ASU 2018-14 is for annual reporting periods ending after December 15, 2020. The ASU has not yet been adopted; however, it is not expected to have a material impact on our company's consolidated financial position, cash flows or results of operations.ASU 2018-15, Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service ContractIn August 2018, the FASB issued ASU 2018-15, Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. ASU 2018-15 amends ASC 350 to include implementation costs of a cloud computing arrangement that is a service contract and clarifies that a customer should apply ASC 350-40 to determine which implementation costs should be capitalized in a cloud computing arrangement that is considered a service contract. The effective date of ASU 2018-15 is for interim and annual reporting periods beginning after December 15, 2019. The ASU has not yet been adopted; however, it is not expected to have a material impact on our company's consolidated financial position, cash flows or results of operations. |

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| - 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
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