Condensed Financial Statements Of Parent Company Condensed Statements Of Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Investment income, net of expenses									$ 609	$ 595	$ 572
Realized investment gains, net									148	124	70
Other revenues									5	5	7
Total revenues	$ 1,411	$ 1,412	$ 1,386	$ 1,523	$ 1,312	$ 1,402	$ 1,371	$ 1,364	5,732	5,449	5,142
Expenses
Interest expense									53	53	53
Other expenses									13	12	13
Total expenses									5,002	4,637	4,261
Income (Loss) Before Income Taxes and Earnings of Subsidiaries	197	129	128	276	128	253	166	265	730	812	881
Benefit for income taxes									(315)	221	247
Net Income	$ 642	$ 102	$ 100	$ 201	$ 100	$ 180	$ 123	$ 188	1,045	591	634
Cincinnati Financial Corporation
Revenues
Investment income, net of expenses									62	56	53
Realized investment gains, net									28	27	(19)
Other revenues									15	15	15
Total revenues									105	98	49
Expenses
Interest expense									52	52	52
Other expenses									28	27	28
Total expenses									80	79	80
Income (Loss) Before Income Taxes and Earnings of Subsidiaries									25	19	(31)
Benefit for income taxes									(161)	(6)	(23)
Net Income (Loss) Before Earnings of Subsidiaries									186	25	(8)
Increase in equity of subsidiaries									859	566	642
Net Income									$ 1,045	$ 591	$ 634