Condensed Financial Statements Of Parent Company Condensed Statements Of Cash Flows (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 421	$ 164	$ 375
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	44	42	41
Realized gains on investments, net	(42)	(70)	(159)
Changes in:
Investment income receivable	4		(1)
Current income tax receivable/payable	79	(25)	(73)
Other assets	(4)	2	3
Other liabilities	78	(49)	(18)
Net cash provided by operating activities	638	247	531
CASH FLOWS FROM INVESTING ACTIVITIES
Sale of fixed-maturities	144	71	199
Call or maturity of fixed maturities	927	808	886
Sale of equity securities	216	539	273
Purchase of fixed maturities	(1,166)	(1,087)	(1,483)
Purchase of equity securities	(425)	(337)	(396)
Change in short-term investments, net			7
Investment in buildings and equipment, net	(6)	(7)	(17)
Change in other invested assets, net	5	7
Net cash provided by investing activities	(304)	(8)	(529)
CASH FLOWS FROM FINANCING ACTIVITIES
Increase in notes payable		55
Payment of cash dividends to shareholders	(256)	(255)	(252)
Proceeds from stock options exercised	10	1	0
Other	(13)	(11)	(10)
Net cash used in financing activities	(285)	(186)	(174)
Net increase (decrease) in cash and cash equivalents	49	53	(172)
Cash and cash equivalents at beginning of year	438	385	557
Cash and cash equivalents at end of period	487	438	385
Cincinnati Financial Corporation [Member]
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	421	164	375
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	7	7	7
Realized gains on investments, net	(34)	(15)	(17)
Dividends from subsidiaries	300	180	220
Changes in:
Increase in equity of subsidiaries	(406)	(163)	(372)
Investment income receivable	1	1
Current federal income taxes	(24)	25	3
Current income tax receivable/payable	18	(10)	2
Other assets	(2)	2
Other liabilities	7	(23)	(12)
Net cash provided by operating activities	288	168	206
CASH FLOWS FROM INVESTING ACTIVITIES
Sale of fixed-maturities	114	5	32
Call or maturity of fixed maturities	13	13	21
Sale of equity securities	111	101	85
Purchase of fixed maturities	(1)		(27)
Purchase of equity securities	(212)	(78)	(92)
Investment in buildings and equipment, net	(1)	(1)
Change in other invested assets, net	4	5
Net cash provided by investing activities	28	45	19
CASH FLOWS FROM FINANCING ACTIVITIES
Increase in notes payable		55
Payment of cash dividends to shareholders	(256)	(255)	(252)
Purchase of treasury shares		(32)	(10)
Proceeds from stock options exercised	9	(4)	(2)
Net transfers to subsidiaries	(2)	2	21
Other	3	3	2
Net cash used in financing activities	(246)	(231)	(241)
Net increase (decrease) in cash and cash equivalents	70	(18)	(16)
Cash and cash equivalents at beginning of year	20	38	54
Cash and cash equivalents at end of period	$ 90	$ 20	$ 38