| **Shareholders' Equity And Dividend Restrictions**           | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         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| **Shareholders Equity And Dividend Restrictions [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             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| Shareholders' Equity And Dividend Restrictions               | Shareholders’ Equity and Dividend RestrictionsDeclared cash dividends per share were $1.76, $1.655 and $1.62 for the years ended December 31, 2014, 2013 and 2012, respectively.Our insurance subsidiary declared dividends to the parent company of $400 million in 2014, $375 million in 2013 and $300 million in 2012. State regulatory requirements restrict the dividends insurance subsidiaries can pay. Dividends must be paid within 30 days of declaration. Generally, the most our insurance subsidiary can pay without prior regulatory approval is the greater of 10 percent of statutory capital and surplus or 100 percent of statutory net income for the prior calendar year. Dividends exceeding these limitations may be paid only with approval of the insurance department of the domiciliary state. During 2015, the total that our insurance subsidiary, which is the parent of all other insurance subsidiaries, may declare in dividends is approximately $447 million. Accumulated Other Comprehensive IncomeThe table below shows beginning and end of year accumulated other comprehensive income or loss for investments, pension obligations, life deferred acquisition costs, life policy reserves and other. The changes from the beginning of year to the end of year are the result of changes to other comprehensive income or loss (OCI). (Dollars in millions) 2014  2013  2012  Beforetax Incometax Net  Beforetax Incometax Net  Beforetax Incometax NetInvestments:                    AOCI, January 1 $2,335 $808 $1,527  $1,875 $647 $1,228  $1,489 $512 $977OCI before realized gains recognized in net income 514 181 333  537 188 349  426 149 277Realized gains recognized in net income (130) (47) (83)  (77) (27) (50)  (40) (14) (26)OCI 384 134 250  460 161 299  386 135 251AOCI, December 31 $2,719 $942 $1,777  $2,335 $808 $1,527  $1,875 $647 $1,228                     Pension Obligations:                    AOCI, January 1 $(18) $(6) $(12)  $(101) $(35) $(66)  $(88) $(31) $(57)OCI before realized losses recognized in net income (21) (7) (14)  83 29 54  (13) (4) (9)Realized losses recognized in net income 3 1 2  — — —  — — —OCI (18) (6) (12)  83 29 54  (13) (4) (9)AOCI, December 31 $(36) $(12) $(24)  $(18) $(6) $(12)  $(101) $(35) $(66)                     Life deferred acquisition costs, life policy reserves and other:                    AOCI, January 1 $(16) $(5) $(11)  $(50) $(17) $(33)  $(29) $(10) $(19)OCI before realized gains recognized in net income 7 3 4  40 14 26  (19) (7) (12)Realized gains recognized in net income (3) (1) (2)  (6) (2) (4)  (2) — (2)OCI 4 2 2  34 12 22  (21) (7) (14)AOCI, December 31 $(12) $(3) $(9)  $(16) $(5) $(11)  $(50) $(17) $(33)                     Summary of AOCI:                    AOCI, January 1 $2,301 $797 $1,504  $1,724 $595 $1,129  $1,372 $471 $901Investments OCI 384 134 250  460 161 299  386 135 251Pension obligations OCI (18) (6) (12)  83 29 54  (13) (4) (9)Life deferred acquisition costs, life policy reserves and other OCI 4 2 2  34 12 22  (21) (7) (14)Total OCI 370 130 240  577 202 375  352 124 228AOCI, December 31 $2,671 $927 $1,744  $2,301 $797 $1,504  $1,724 $595 $1,129                      |

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| - Definition
Shareholders' Equity And Accumulated Other Comprehensive Income
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| - Details**Name:**cinf_ShareholdersEquityAndDividendRestrictionsAbstract**Namespace Prefix:**cinf_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |