| **Shareholders' Equity And Dividend Restrictions (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions** | 12 Months Ended |
|-----------------------------------------------------------------------------------------------------------------------|-----------------|
||
| Declared cash dividends, per share                                                                                    | $ 2.76          | $ 2.52 | $ 2.40 |
| Dividend payment without prior regulatory approval, maximum percent of policyholder surplus                           | 10.00%          |   |   |
| Dividend payment without prior regulatory approval, percent of statutory net income for the prior calendar year       | 100.00%         |   |   |
| Dividends might be paid during next year                                                                              | $ 651           |   |   |
| The Cincinnati Insurance Company                                                                                      |            |   |   |
| Cash Dividends Paid to Parent                                                                                         | 729             | $ 583 | $ 550 |
| Cincinnati Global                                                                                                     |            |   |   |
| Cash Dividends Paid to Parent                                                                                         | $ 0             | $ 0 | $ 0 |

| X                                                                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Minimum percent of policyholder surplus that our insurance subsidiary can pay to the parent without prior regulatory approval.
+ References
No definition available.
+ Details**Name:**cinf_DividendToParent**Namespace Prefix:**cinf_**Data Type:**dtr-types:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Maximum percentage of statutory net income that our insurance subsidiary can pay to the parent without prior regulatory approval.
+ References
No definition available.
+ Details**Name:**cinf_PercentageOfStatutoryNetIncomeFromPriorYear**Namespace Prefix:**cinf_**Data Type:**dtr-types:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This element represents disclosure of the aggregate cash dividends paid to the entity by consolidated subsidiaries.
+ References
Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04(b)) -URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690
+ Details**Name:**us-gaap_CashDividendsPaidToParentCompanyByConsolidatedSubsidiaries**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Aggregate dividends declared during the period for each share of common stock outstanding.
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI https://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770
+ Details**Name:**us-gaap_CommonStockDividendsPerShareDeclared**Namespace Prefix:**us-gaap_**Data Type:**dtr-types:perShareItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of dividends available for payment after computation of statutory restrictions on capital surplus.
+ References
No definition available.
+ Details**Name:**us-gaap_StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPayments**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**dei_LegalEntityAxis=cinf_CincinnatiInsuranceCompanyMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**dei_LegalEntityAxis=cinf_CincinnatiGlobalUnderwritingLtd.Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |