Condensed Financial Statements Of Parent Company Condensed Statements Of Cash Flows (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
Cash Flows From Operating Activities
Net Income	$ 1,049	$ 484	$ 909	$ (1,226)	$ 626	$ 248	$ 428	$ 695	$ 1,216	$ 1,997	$ 287
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization									81	72	63
Gain (Loss) on Sale of Investments									(851)	(1,640)	408
Changes in:
Investment income receivable									(3)	(1)	2
Current income tax receivable/payable									44	92	(91)
Other assets									(26)	(22)	(1)
Net cash provided by operating activities									1,491	1,208	1,181
Cash Flows From Investing Activities
Sale of fixed maturities									179	102	36
Call or maturity of fixed maturities									912	1,241	1,127
Sale of equity securities									515	203	403
Purchase of fixed maturities									(1,382)	(1,742)	(1,510)
Purchase of equity securities									(699)	(382)	(441)
Investment in buildings and equipment									(20)	(24)	(20)
Change in other invested assets, net									(50)	(72)	(38)
Net cash used in investing activities									(560)	(679)	(451)
Cash Flows From Financing Activities
Payment of cash dividends to shareholders									(375)	(355)	(336)
Shares acquired - share repurchase authorization									(261)	(67)	(125)
Proceeds from stock options exercised										11	9
Other									(110)	(54)	(60)
Net cash used in financing activities									(798)	(546)	(603)
Cash and cash equivalents at beginning of year				767				784	767	784	657
Cash and cash equivalents at end of year	900				767				900	767	784
Cincinnati Financial Corporation
Cash Flows From Operating Activities
Net Income									1,216	1,997	287
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization									12	10	7
Gain (Loss) on Sale of Investments									(552)	(720)	114
Dividends from subsidiaries									550	625	500
Changes in:
Increase in equity of subsidiaries									(763)	(1,414)	(367)
Investment income receivable									(1)	(1)	2
Current federal income taxes									(3)	(1)	14
Current income tax receivable/payable									91	146	(35)
Other assets									0	4	(17)
Other liabilities									1	4	3
Intercompany receivable for operations									34	20	19
Net cash provided by operating activities									585	670	527
Cash Flows From Investing Activities
Sale of fixed maturities									0	3	1
Call or maturity of fixed maturities									1	21	19
Sale of equity securities									307	122	131
Purchase of fixed maturities									(23)	(39)	(17)
Purchase of equity securities									(372)	(237)	(177)
Investment in buildings and equipment									(11)	(13)	(12)
Cash paid for acquisition									0
Change in other invested assets, net									(42)	(67)	(11)
Net cash used in investing activities									(140)	(273)	(66)
Cash Flows From Financing Activities
Payment of cash dividends to shareholders									(375)	(355)	(336)
Shares acquired - share repurchase authorization									(261)	(67)	(125)
Proceeds from stock options exercised									7	11	9
Other									3	2	1
Net cash used in financing activities									(626)	(409)	(451)
Net change in cash and cash equivalents									(181)	(12)	10
Cash and cash equivalents at beginning of year				$ 197				$ 209	197	209	199
Cash and cash equivalents at end of year	$ 16				$ 197				$ 16	$ 197	$ 209