Condensed Financial Statements Of Parent Company Condensed Statements Of Cash Flows (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
Cash Flows From Operating Activities
Net Income	$ 642	$ 102	$ 100	$ 201	$ 100	$ 180	$ 123	$ 188	$ 1,045	$ 591	$ 634
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization									55	48	52
Realized investment gains, net									(148)	(124)	(70)
Changes in:
Investment income receivable									0	(5)	(6)
Current income tax receivable/payable									67	(35)	(18)
Other assets									(43)	34	(39)
Other liabilities									24	61	55
Net cash provided by operating activities									1,052	1,115	1,075
Cash Flows From Investing Activities
Sale of fixed maturities									23	15	43
Call or maturity of fixed maturities									1,172	1,511	1,199
Sale of equity securities									523	465	342
Purchase of fixed maturities									(1,723)	(1,994)	(1,722)
Purchase of equity securities									(513)	(439)	(493)
Investment in buildings and equipment									(16)	(13)	(10)
Change in other invested assets, net									(15)	(14)	1
Net cash used in investing activities									(558)	(456)	(624)
Cash Flows From Financing Activities
Changes in note payable									4	(15)	(14)
Payment of cash dividends to shareholders									(400)	(306)	(366)
Shares acquired - share repurchase authorization									(92)	(39)	(53)
Proceeds from stock options exercised									13	21	24
Other									(54)	(32)	(28)
Net cash used in financing activities									(614)	(426)	(498)
Net change in cash and cash equivalents									(120)	233	(47)
Cash and cash equivalents at beginning of year				777				544	777	544	591
Cash and cash equivalents at end of year	657				777				657	777	544
Cincinnati Financial Corporation
Cash Flows From Operating Activities
Net Income									1,045	591	634
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization									7	6	7
Realized investment gains, net									(28)	(27)	19
Dividends from subsidiaries									465	475	447
Changes in:
Increase in equity of subsidiaries									(859)	(566)	(642)
Investment income receivable									0	(2)	0
Current federal income taxes									(5)	(4)	(7)
Current income tax receivable/payable									(150)	8	(10)
Other assets									(20)	(4)	(3)
Other liabilities									15	(1)	13
Intercompany receivable for operations									13	20	16
Net cash provided by operating activities									483	496	474
Cash Flows From Investing Activities
Call or maturity of fixed maturities									14	5	8
Sale of equity securities									230	135	54
Purchase of fixed maturities									(2)	0	0
Purchase of equity securities									(293)	(175)	(110)
Investment in buildings and equipment									(3)	(2)	0
Change in other invested assets, net									0	6	1
Net cash used in investing activities									(54)	(31)	(47)
Cash Flows From Financing Activities
Payment of cash dividends to shareholders									(400)	(306)	(366)
Shares acquired - share repurchase authorization									(92)	(39)	(53)
Proceeds from stock options exercised									13	21	24
Other									1	1	2
Net cash used in financing activities									(478)	(323)	(393)
Net change in cash and cash equivalents									(49)	142	34
Cash and cash equivalents at beginning of year				$ 248				$ 106	248	106	72
Cash and cash equivalents at end of year	$ 199				$ 248				$ 199	$ 248	$ 106