| **Consolidated Statements Of Comprehensive Income (USD $)In Millions, unless otherwise specified**                       | 12 Months Ended                                                                                                                               |
|--------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Statement of Comprehensive Income [Abstract]**                                                                         |                                                                                                                                          |   |   |
| Net Income                                                                                                               | $ 525us-gaap_NetIncomeLoss                                                                                                                    | $ 517us-gaap_NetIncomeLoss | $ 421us-gaap_NetIncomeLoss |
| **Other Comprehensive Income**                                                                                           |                                                                                                                                          |   |   |
| Unrealized gains on investments, net of tax of $134, $161, and $135, respectively                                        | 250us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax                                          | 299us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax | 251us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax |
| Amortization of pension actuarial loss and prior service cost, net of tax of $(6), $29, and $(4), respectively           | (12)cinf_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetActuarialLossAndPriorServiceCostArisingDuringPeriodBeforeTax | 54cinf_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetActuarialLossAndPriorServiceCostArisingDuringPeriodBeforeTax | (9)cinf_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetActuarialLossAndPriorServiceCostArisingDuringPeriodBeforeTax |
| Change in life deferred acquisition costs, life policy reserves and other, net of tax of $2, $12, and $(7), respectively | 2cinf_OtherComprehensiveIncomeChangeInLifeDeferredAcquistionCostsLifePolicyReservesAndOtherNetOfTax                                           | 22cinf_OtherComprehensiveIncomeChangeInLifeDeferredAcquistionCostsLifePolicyReservesAndOtherNetOfTax | (14)cinf_OtherComprehensiveIncomeChangeInLifeDeferredAcquistionCostsLifePolicyReservesAndOtherNetOfTax |
| Other comprehensive income, net of tax                                                                                   | 240us-gaap_OtherComprehensiveIncomeLossNetOfTax                                                                                               | 375us-gaap_OtherComprehensiveIncomeLossNetOfTax | 228us-gaap_OtherComprehensiveIncomeLossNetOfTax |
| Comprehensive Income                                                                                                     | $ 765us-gaap_ComprehensiveIncomeNetOfTax                                                                                                      | $ 892us-gaap_ComprehensiveIncomeNetOfTax | $ 649us-gaap_ComprehensiveIncomeNetOfTax |

| X                                                                                                                                                                                                                                                                                                                                                                                                    |
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| - Definition
Other Comprehensive Income, Change in Life Deferred Acquistion Costs, Life Policy Reserves and Other, Net of Tax
+ References
No definition available.
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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         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| - Definition
Condensed Consolidated Statements of Comprehensive Operations (USD $) In Millions, except Per Share data, unless otherwise specified 3 Months Ended 9 Months Ended Sep. 30, 2012 Sep. 30, 2011 Sep. 30, 2012 Sep. 30, 2011 REVENUES Earned premiums $ 889 $ 812 $ 2,605 $ 2,367 Investment income, net of expenses 132 130 395 393 Total realized investment gains (losses), net 10 (2) 29 77 Fee revenues 1 1 4 3 Other revenues 3 3 8 8 Total revenues 1,035 944 3,041 2,848 BENEFITS AND EXPENSES Insurance losses and policyholder benefits 571 656 1,840 2,032 Underwriting, acquisition and insurance expenses 296 260 857 775 Interest expense 14 13 41 40 Other operating expenses 2 4 10 14 Total benefits and expenses 883 933 2,748 2,861 INCOME (LOSS) BEFORE INCOME TAXES 152 11 293 (13) PROVISION (BENEFIT) FOR INCOME TAXES Current 34 17 60 (9) Deferred 7 (25) 4 (34) Provision (benefit) for income taxes 41 (8) 64 (43) NET INCOMEX - DefinitionThe portion of profit or loss for the period, net of income taxes, which is attributable to the parent. + ReferencesReference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 19 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.22) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Other Comprehensive Income -URI http://asc.fasb.org/extlink&oid=6519514 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.18) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 10, 15 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. 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+ References
No definition available.
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| - Definition
Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.
+ References
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| - Definition
The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.
+ References
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| - Definition
Amount after tax and reclassification adjustments of other comprehensive income (loss).
+ References
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| - Definition
Amount before tax and reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.
+ References
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