Condensed Financial Statements Of Parent Company Condensed Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions
Fixed maturities, amortized cost	$ 10,314	$ 9,799
Investments
Fixed maturities, at fair value (amortized cost: 2017—$35; 2016—$46)	10,699	10,085
Equity securities, at fair value (cost: 2017—$1,159; 2016—$1,084)	6,249	5,334
Other invested assets	103	81
Total investments	17,051	15,500
Cash and cash equivalents	657	777	$ 544	$ 591
Investment income receivable	134	134
Land, building and equipment, net, for company use (accumulated depreciation: 2017—$115; 2016—$111)	185	183
Other assets	216	198
Total assets	21,843	20,386
Liabilities
Deferred federal income tax	995	1,279
Long-term debt	787	787
Other liabilities	792	786
Total liabilities	13,600	13,326
Shareholders' Equity
Common stock	397	397
Paid-in capital	1,265	1,252
Retained earnings	5,180	5,037
Accumulated other comprehensive income	2,788	1,693
Treasury stock at cost	(1,387)	(1,319)
Total shareholders' equity	8,243	7,060	6,427
Total liabilities and shareholders' equity	21,843	20,386
Equity securities, cost	3,094	2,995
Cincinnati Financial Corporation
Condensed Financial Statements, Captions
Fixed maturities, amortized cost	35	46
Investments
Fixed maturities, at fair value (amortized cost: 2017—$35; 2016—$46)	37	52
Equity securities, at fair value (cost: 2017—$1,159; 2016—$1,084)	2,275	1,833
Other invested assets	35	29
Total investments	2,347	1,914
Cash and cash equivalents	199	248	$ 106	$ 72
Equity in net assets of subsidiaries	6,542	5,790
Investment income receivable	8	8
Land, building and equipment, net, for company use (accumulated depreciation: 2017—$115; 2016—$111)	130	132
Income tax receivable	15	10
Other assets	52	35
Due from subsidiaries	107	106
Total assets	9,400	8,243
Liabilities
Dividends declared but unpaid	82	79
Deferred federal income tax	234	252
Long-term debt	787	787
Other liabilities	54	65
Total liabilities	1,157	1,183
Shareholders' Equity
Common stock	397	397
Paid-in capital	1,265	1,252
Retained earnings	5,180	5,037
Accumulated other comprehensive income	2,788	1,693
Treasury stock at cost	(1,387)	(1,319)
Total shareholders' equity	8,243	7,060
Total liabilities and shareholders' equity	9,400	8,243
Equity securities, cost	$ 1,159	$ 1,084