Condensed Financial Statements Of Parent Company Condensed Statements Of Cash Flows (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
Cash Flows From Operating Activities
Net Income	$ (452)	$ 553	$ 217	$ (31)	$ 642	$ 102	$ 100	$ 201	$ 287	$ 1,045	$ 591
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization									63	55	48
Gain (Loss) on Sale of Investments									408	(148)	(124)
Changes in:
Investment income receivable									2	0	(5)
Current income tax receivable/payable									(91)	67	(35)
Other assets									(1)	(43)	34
Other liabilities									0	24	61
Net cash provided by operating activities									1,181	1,052	1,115
Cash Flows From Investing Activities
Sale of fixed maturities									36	23	15
Call or maturity of fixed maturities									1,127	1,172	1,511
Sale of equity securities									403	523	465
Purchase of fixed maturities									(1,510)	(1,723)	(1,994)
Purchase of equity securities									(441)	(513)	(439)
Investment in buildings and equipment									(20)	(16)	(13)
Change in other invested assets, net									(38)	(15)	(14)
Net cash used in investing activities									(451)	(558)	(456)
Cash Flows From Financing Activities
Changes in note payable									8	4	(15)
Payment of cash dividends to shareholders									(336)	(400)	(306)
Shares acquired - share repurchase authorization									(125)	(92)	(39)
Proceeds from stock options exercised									9	13	21
Other									(60)	(54)	(32)
Net cash used in financing activities									(603)	(614)	(426)
Net change in cash and cash equivalents									127	(120)	233
Cash and cash equivalents at beginning of year				657				777	657	777	544
Cash and cash equivalents at end of year	784				657				784	657	777
Cincinnati Financial Corporation
Cash Flows From Operating Activities
Net Income									287	1,045	591
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization									7	7	6
Gain (Loss) on Sale of Investments									114	(28)	(27)
Dividends from subsidiaries									500	465	475
Changes in:
Increase in equity of subsidiaries									(367)	(859)	(566)
Investment income receivable									2	0	(2)
Current federal income taxes									14	(5)	(4)
Current income tax receivable/payable									(35)	(150)	8
Other assets									(17)	(20)	(4)
Other liabilities									3	15	(1)
Intercompany receivable for operations									19	13	20
Net cash provided by operating activities									527	483	496
Cash Flows From Investing Activities
Sale of fixed maturities									1	0	0
Call or maturity of fixed maturities									19	14	5
Sale of equity securities									131	230	135
Purchase of fixed maturities									(17)	(2)	0
Purchase of equity securities									(177)	(293)	(175)
Investment in buildings and equipment									(12)	(3)	(2)
Change in other invested assets, net									(11)	0	6
Net cash used in investing activities									(66)	(54)	(31)
Cash Flows From Financing Activities
Payment of cash dividends to shareholders									(336)	(400)	(306)
Shares acquired - share repurchase authorization									(125)	(92)	(39)
Proceeds from stock options exercised									9	13	21
Other									1	1	1
Net cash used in financing activities									(451)	(478)	(323)
Net change in cash and cash equivalents									10	(49)	142
Cash and cash equivalents at beginning of year				$ 199				$ 248	199	248	106
Cash and cash equivalents at end of year	$ 209				$ 199				$ 209	$ 199	$ 248