Commitments and Contingent Liabilities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015
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