Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification included in financing activities	$ (124)	$ (88)
Excess tax benefit	6
Accounting Standards Update 2016-09, Excess Tax Benefit Component [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification included in financing activities	11	$ 8
Cumulative effect adjustment	$ 0

Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount

No definition available.

Name:	cinf_EffectiveIncomeTaxRateReconciliationSharebasedCompensationExcessTaxBenefitAmount
Namespace Prefix:	cinf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

+ References

No definition available.

+ Details

Name:	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of cash inflow (outflow) from financing activities, including discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3521-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 26
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3574-108585

+ Details

Name:	us-gaap_NetCashProvidedByUsedInFinancingActivities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=cinf_AccountingStandardsUpdate201609ExcessTaxBenefitComponentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: