Statutory Accounting Information (Schedule Of Statutory Net Income And Statutory Surplus (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
The Cincinnati Insurance Company
Statutory Accounting Practices
SAP net income (loss)	$ 434	$ 534	$ 436
Capital and surplus	4,686	4,412
The Cincinnati Casualty Company
Statutory Accounting Practices
SAP net income (loss)	11	12	12
Capital and surplus	360	337
The Cincinnati Indemnity Company
Statutory Accounting Practices
SAP net income (loss)	4	3	3
Capital and surplus	93	88
The Cincinnati Specialty Underwriters Insurance Company
Statutory Accounting Practices
SAP net income (loss)	57	49	32
Capital and surplus	372	306
The Cincinnati Life Insurance Company
Statutory Accounting Practices
SAP net income (loss)	2	(11)	$ (19)
Capital and surplus	$ 200	$ 208