Statutory Accounting Information (Schedule Of Statutory Net Income And Statutory Surplus (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cincinnati Insurance Company [Member]
Statutory Accounting Practices [Line Items]
SAP Net Income (Loss)	$ 334	$ 120	$ 318
Capital and Surplus	3,914	3,747
Cincinnati Casualty Company [Member]
Statutory Accounting Practices [Line Items]
SAP Net Income (Loss)	10	15	10
Capital and Surplus	293	280
Cincinnati Indemnity Company [Member]
Statutory Accounting Practices [Line Items]
SAP Net Income (Loss)	2	2	2
Capital and Surplus	76	73
Cincinnati Specialty Underwriters Insurance Company [Member]
Statutory Accounting Practices [Line Items]
SAP Net Income (Loss)	6	11	1
Capital and Surplus	199	186
Cincinnati Life Insurance Company [Member]
Statutory Accounting Practices [Line Items]
SAP Net Income (Loss)	5	(13)	15
Capital and Surplus	$ 276	$ 281