2.4.0.82402404 - Disclosure - Investments - Realized Investment Gains and Losses and Change in Unrealized Investment Gains and Losses and Other Items (Detail)truefalseIn Millions, unless otherwise specifiedfalse1false USDfalsefalse$D2013Q2QTDhttp://www.sec.gov/CIK0000020286duration2013-04-01T00:00:002013-06-30T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$2false USDfalsefalse$D2012Q2QTDhttp://www.sec.gov/CIK0000020286duration2012-04-01T00:00:002012-06-30T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$3false USDfalsefalse$D2013Q2YTDhttp://www.sec.gov/CIK0000020286duration2013-01-01T00:00:002013-06-30T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$4false USDfalsefalse$D2012Q2YTDhttp://www.sec.gov/CIK0000020286duration2012-01-01T00:00:002012-06-30T00:00:00usdStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$1true 4us-gaap_NetInvestmentIncomeAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Investment income summary:2false 5us-gaap_InvestmentIncomeInterestus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse103000000103USD$falsetruefalse2truefalsefalse106000000106USD$falsetruefalse3truefalsefalse205000000205USD$falsetruefalse4truefalsefalse212000000212USD$falsetruefalsexbrli:monetaryItemTypemonetaryAmount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(b)) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 false2Interest on fixed maturities3false 5us-gaap_InvestmentIncomeDividendus-gaap_truecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1truefalsefalse3000000030USD$falsefalsefalse2truefalsefalse2700000027USD$falsefalsefalse3truefalsefalse5700000057USD$falsefalsefalse4truefalsefalse5300000053USD$falsefalsefalsexbrli:monetaryItemTypemonetaryAmount of dividend income on nonoperating securities.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(a)) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 false2Dividends on equity securities4false 5cinf_InvestmentIncomeOtherLongTermInvestmentscinf_falsecreditdurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsefalse00USD$falsefalsefalse2truefalsefalse10000001USD$falsefalsefalse3truefalsefalse10000001USD$falsefalsefalse4truefalsefalse20000002USD$falsefalsefalsexbrli:monetaryItemTypemonetaryIncome derived from those other than interest and dividends.No definition available.false2Other investment income5false 5cinf_GrossInvestmentIncomecinf_falsecreditdurationfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse133000000133USD$falsefalsefalse2truefalsefalse134000000134USD$falsefalsefalse3truefalsefalse263000000263USD$falsefalsefalse4truefalsefalse267000000267USD$falsefalsefalsexbrli:monetaryItemTypemonetaryIncome derived from investments in debt and equity securities, cash and cash equivalents, and other long-term investments. 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