Accounting Policies (Details) $ in Millions	Dec. 31, 2019 USD ($)
Accounting Policies [Abstract]
Increase to allowance through retained earnings for ASU 2016-13, after-tax	$ 2

Increase to allowance through retained earnings for ASU 2016-13, after-tax

No definition available.

Name:	cinf_IncreasetoallowancethroughretainedearningsforASU201613aftertax
Namespace Prefix:	cinf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant