Commitments and Contingent Liabilities (Narrative) (Details) (Maximum, USD $)	3 Months Ended
Mar. 31, 2013
Maximum
Loss Contingencies [Line Items]
Estimate for which the risk of loss is more than remote	$ 500,000

Estimate for which the risk of loss is more than remote

No definition available.

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