Commitments and Contingent Liabilities (Narrative) (Details) $ in Millions	9 Months Ended
Sep. 30, 2015 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Estimate for which the risk of loss is more than remote but not probable	$ 1

Estimate for which the risk of loss is more than remote but not probable

No definition available.

Name:	cinf_EstimateforWhichTheRiskofLossisMorethanRemoteButNotProbable
Namespace Prefix:	cinf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration