Condensed Financial Statements Of Parent Company Condensed Statements Of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions
Net Income	$ (452)	$ 553	$ 217	$ (31)	$ 642	$ 102	$ 100	$ 201	$ 287	$ 1,045	$ 591
Unrealized gains and (losses) on investments available for sale									(267)	598	345
Unrealized gains and (losses) on investments available for sale, investments held by subsidiaries and other									(330)	914	521
Amortization of pension actuarial gains (losses) and prior service cost									(4)	14	16
OCI									(334)	928	537
Income taxes on above of other comprehensive income (loss)									(71)	325	188
Other comprehensive income (loss), net of tax									(263)	603	349
Comprehensive Income									24	1,648	940
Cincinnati Financial Corporation
Condensed Financial Statements, Captions
Net Income									287	1,045	591
Unrealized gains and (losses) on investments available for sale									(110)	391	221
Unrealized gains and (losses) on investments held by subsidiaries									(631)	672	434
Reclassification adjustment for (gains) and losses included in net income									108	(28)	(27)
Reclassification adjustment for (gains) included in net income on subsidiaries									294	(120)	(97)
Unrealized (losses) and gains on other									0	(2)	(6)
Unrealized gains and (losses) on other subsidiaries									$ 9	$ 1	$ (4)