| **Accumulated Other Comprehensive Income (Tables)**       | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             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| **Accumulated Other Comprehensive Income [Abstract]**     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       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| Schedule of Accumulated Other Comprehensive Income (Loss) | (Dollars in millions) Three months ended June 30,  2016  2015  Before tax Income tax Net  Before tax Income tax NetInvestments:             AOCI, beginning of period $2,384 $822 $1,562  $2,676 $927 $1,749OCI before realized gains recognized in net income 331 118 213  (260) (91) (169)Realized gains recognized in net income (42) (15) (27)  (59) (21) (38)OCI 289 103 186  (319) (112) (207)AOCI, end of period $2,673 $925 $1,748  $2,357 $815 $1,542              Pension obligations:             AOCI, beginning of period $(41) $(13) $(28)  $(35) $(12) $(23)OCI excluding amortization recognized in net income — — —  — — —Amortization recognized in net income 1 — 1  2 1 1OCI 1 — 1  2 1 1AOCI, end of period $(40) $(13) $(27)  $(33) $(11) $(22)              Life deferred acquisition costs, life policy reserves and other:             AOCI, beginning of period $(3) $— $(3)  $(14) $(4) $(10)OCI before realized gains recognized in net income (5) (2) (3)  7 3 4Realized gains recognized in net income (2) (1) (1)  (1) (1) —OCI (7) (3) (4)  6 2 4AOCI, end of period $(10) $(3) $(7)  $(8) $(2) $(6)              Summary of AOCI:             AOCI, beginning of period $2,340 $809 $1,531  $2,627 $911 $1,716Investments OCI 289 103 186  (319) (112) (207)Pension obligations OCI 1 — 1  2 1 1Life deferred acquisition costs, life policy reserves and other OCI (7) (3) (4)  6 2 4Total OCI 283 100 183  (311) (109) (202)AOCI, end of period $2,623 $909 $1,714  $2,316 $802 $1,514              (Dollars in millions)Six months ended June 30, 2016  2015 Before tax Income tax Net  Before tax Income tax NetInvestments:            AOCI, beginning of period$2,094 $722 $1,372  $2,719 $942 $1,777OCI excluding realized gains recognized in net income682 239 443  (257) (90) (167)Realized gains recognized in net income(103) (36) (67)  (105) (37) (68)OCI579 203 376  (362) (127) (235)AOCI, end of period$2,673 $925 $1,748  $2,357 $815 $1,542             Pension obligations:            AOCI, beginning of period$(42) $(14) $(28)  $(36) $(12) $(24)OCI excluding amortization recognized in net income— — —  — — —Amortization recognized in net income2 1 1  3 1 2OCI2 1 1  3 1 2AOCI, end of period$(40) $(13) $(27)  $(33) $(11) $(22)             Life deferred acquisition costs, life policy reserves and other:            AOCI, beginning of period$1 $1 $—  $(12) $(3) $(9)OCI excluding realized gains recognized in net income(9) (3) (6)  6 2 4Realized gains recognized in net income(2) (1) (1)  (2) (1) (1)OCI(11) (4) (7)  4 1 3AOCI, end of period$(10) $(3) $(7)  $(8) $(2) $(6)             Summary of AOCI:            AOCI, beginning of period$2,053 $709 $1,344  $2,671 $927 $1,744Investments OCI579 203 376  (362) (127) (235)Pension obligations OCI2 1 1  3 1 2Life deferred acquisition costs, life policy reserves and other OCI(11) (4) (7)  4 1 3Total OCI570 200 370  (355) (125) (230)AOCI, end of period$2,623 $909 $1,714  $2,316 $802 $1,514              |

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| - Definition
Accumulated Other Comprehensive Income [Abstract]
+ References
No definition available.
+ Details**Name:**cinf_AccumulatedOtherComprehensiveIncomeAbstract**Namespace Prefix:**cinf_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Tabular disclosure of the components of accumulated other comprehensive income (loss).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669686-108580
+ Details**Name:**us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock**Namespace Prefix:**us-gaap_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |