Condensed Financial Statements of Parent Company Condensed Statements of Income (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
REVENUES
Investment income, net of expenses	$ 525		$ 518		$ 501
Total realized investment gains (losses), net	70		159		336
Other revenue	10		9		9
Total revenues	3,803	[1]	3,772	[1]	3,903
EXPENSES
Interest expense	54		54		55
Other expenses	13		16		20
Total benefits and expenses	3,627		3,271		3,321
INCOME BEFORE INCOME TAXES	176		501		582
PROVISION (BENEFIT) FOR INCOME TAXES	10		124		150
NET INCOME	166		377		432
Cincinnati Financial Corporation
REVENUES
Investment income, net of expenses	41		41		41
Total realized investment gains (losses), net	15		17		135
Other revenue	14		14		15
Total revenues	70		72		191
EXPENSES
Interest expense	53		52		52
Other expenses	25		24		27
Total benefits and expenses	78		76		79
INCOME BEFORE INCOME TAXES	(8)		(4)		112
PROVISION (BENEFIT) FOR INCOME TAXES	(9)		(7)		32
NET INCOME BEFORE EARNINGS OF SUBSIDIARIES	1		3		80
Increase in equity of subsidiaries	165		374		352
NET INCOME	$ 166		$ 377		$ 432

[1] Revenues including realized investment gains and losses, which are integral to our financial results over the long term, may cause this value to fluctuate substantially because we have substantial discretion in the timing of investment sales. Also, applicable accounting standards require us to recognize gains and losses from certain changes in fair values of securities and embedded derivatives without actual realization of those gains and losses. We discuss realized investment gains for the past three years in Item 7, Investments Results of Operations, Page 81.