Condensed Financial Statements Of Parent Company Condensed Balance Sheets (Parenthetical) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions
Fixed maturities, amortized cost	$ 10,314	$ 9,799
Equity securities, cost	3,094	2,995
Land, building and equipment, accumulated depreciation	253	237
Cincinnati Financial Corporation
Condensed Financial Statements, Captions
Fixed maturities, amortized cost	35	46
Equity securities, cost	1,159	1,084
Land, building and equipment, accumulated depreciation	$ 115	$ 111