Condensed Financial Statements Of Parent Company Condensed Statements Of Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues
Investment income, net of expenses									$ 670	$ 646	$ 619
Investment gains and losses, net									865	1,650	(402)
Other revenues									10	9	5
Total revenues	$ 2,694	$ 2,227	$ 2,714	$ (99)	$ 2,152	$ 1,700	$ 1,913	$ 2,159	7,536	7,924	5,407
Expenses
Interest expense									54	53	53
Other expenses									20	23	16
Total expenses									6,037	5,452	5,156
Income (Loss) Before Income Taxes and Earnings of Subsidiaries	1,316	614	1,145	(1,576)	781	294	530	867	1,499	2,472	251
Provision (Benefit) for Income Taxes									283	475	(36)
Net Income	$ 1,049	$ 484	$ 909	$ (1,226)	$ 626	$ 248	$ 428	$ 695	1,216	1,997	287
Amortization of pension actuarial gains and losses and prior service costs									(25)	5	(3)
Other comprehensive income (loss)									321	426	(263)
Comprehensive Income									1,537	2,423	24
Cincinnati Financial Corporation
Revenues
Investment income, net of expenses									81	75	65
Investment gains and losses, net									556	728	(108)
Other revenues									15	15	15
Total revenues									652	818	(28)
Expenses
Interest expense									54	52	52
Other expenses									34	37	31
Total expenses									88	89	83
Income (Loss) Before Income Taxes and Earnings of Subsidiaries									564	729	(111)
Provision (Benefit) for Income Taxes									111	146	(31)
Net Income (Loss) Before Earnings of Subsidiaries									453	583	(80)
Increase in equity of subsidiaries									763	1,414	367
Net Income									1,216	1,997	287
Change in unrealized gain (loss) on securities									0	0	(2)
Amortization of pension actuarial gains and losses and prior service costs									(25)	5	(3)
Other Comprehensive Income (Loss) Before Other Comprehensive Income (Loss) from Subsidiaries									(25)	5	(5)
Other Comprehensive Income (Loss) of subsidiaries									346	421	(258)
Other comprehensive income (loss)									321	426	(263)
Comprehensive Income									$ 1,537	$ 2,423	$ 24