Statutory Accounting Information (Schedule Of Statutory Net Income And Statutory Surplus (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
The Cincinnati Insurance Company
Statutory Accounting Practices
SAP net income (loss)	$ 436	$ 418	$ 334
Capital and surplus	4,472	4,326
The Cincinnati Casualty Company
Statutory Accounting Practices
SAP net income (loss)	12	10	10
Capital and surplus	330	317
The Cincinnati Indemnity Company
Statutory Accounting Practices
SAP net income (loss)	3	2	2
Capital and surplus	86	82
The Cincinnati Specialty Underwriters Insurance Company
Statutory Accounting Practices
SAP net income (loss)	32	18	6
Capital and surplus	266	228
The Cincinnati Life Insurance Company
Statutory Accounting Practices
SAP net income (loss)	(19)	(20)	5
Capital and surplus	$ 223	$ 247