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Fair Value Measurements - Financial Assets and Financial Liabilities Carried at Fair Value (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Financial assets at fair value:    
Fixed maturities $ 18,983us-gaap_MarketableSecuritiesFixedMaturities $ 16,486us-gaap_MarketableSecuritiesFixedMaturities
Equity securities 189us-gaap_MarketableSecuritiesEquitySecurities 141us-gaap_MarketableSecuritiesEquitySecurities
Short-term investments 163us-gaap_OtherShortTermInvestments 631us-gaap_OtherShortTermInvestments
Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 18,983us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 [1] 16,486us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 [2]
Equity securities 189us-gaap_MarketableSecuritiesEquitySecurities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 141us-gaap_MarketableSecuritiesEquitySecurities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Subtotal 19,172us-gaap_MarketableSecurities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 16,627us-gaap_MarketableSecurities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Short-term investments 163us-gaap_OtherShortTermInvestments
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 631us-gaap_OtherShortTermInvestments
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Total financial assets at fair value, excluding separate accounts 20,294ci_TotalFinancialAssetsAtFairValueExcludingSeparateAccounts
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 18,012ci_TotalFinancialAssetsAtFairValueExcludingSeparateAccounts
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Financial liabilities at fair value:    
Total financial liabilities at fair value 930us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 757us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Run-off Settlement Annuity Business [Member] | Fair Value, Measurements, Recurring [Member]    
Financial liabilities at fair value:    
Net appreciation required to adjust future policy benefits for run-off settlement annuity business included in fixed maturities 756ci_UnrealizedAppreciationSettlementAnnuity
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_StatementBusinessSegmentsAxis
= ci_RunoffSettlementAnnuityBusinessMember		 458ci_UnrealizedAppreciationSettlementAnnuity
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_StatementBusinessSegmentsAxis
= ci_RunoffSettlementAnnuityBusinessMember
Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 6us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 [3] 3us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 [4]
Financial liabilities at fair value:    
Derivative liabilities 1us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 [3] 16us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 [4]
Other derivatives [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 5us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 3us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Financial liabilities at fair value:    
Derivative liabilities 1us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 15us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_CashFlowHedgingMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Other derivatives [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 1us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember		 0us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Other derivatives [Member] | Non designated [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 0us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 0us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Financial liabilities at fair value:    
Derivative liabilities 0us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 1us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Guaranteed Minimum Income Benefit [Member]    
Financial liabilities at fair value:    
Percentage of GMIB exposure covered by retrocessional coverage 100.00%ci_PercentReinsuredExternallyGuaranteedMinimumIncomeBenefits
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember		 100.00%ci_PercentReinsuredExternallyGuaranteedMinimumIncomeBenefits
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember
Number of external reinsurers 3ci_CededCreditRiskNumberOfExternalReinsurers
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember		 3ci_CededCreditRiskNumberOfExternalReinsurers
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember
Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 953us-gaap_DerivativeAssets
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember		 [5] 751us-gaap_DerivativeAssets
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember		 [5]
Financial liabilities at fair value:    
Derivative liabilities 929us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember		 741us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember
Federal government and agency [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 954us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		 880us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
State and local government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 1,856us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 2,144us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Foreign government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 1,940us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember		 1,444us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
Corporate [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 13,498us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 10,981us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Mortgage-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 85us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember		 153us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
Other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 650us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember		 884us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember
Fair Value Inputs Level 1 [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 290us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 297us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Equity securities 61us-gaap_MarketableSecuritiesEquitySecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 8us-gaap_MarketableSecuritiesEquitySecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Subtotal 351us-gaap_MarketableSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 305us-gaap_MarketableSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Short-term investments 0us-gaap_OtherShortTermInvestments
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 0us-gaap_OtherShortTermInvestments
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Total financial assets at fair value, excluding separate accounts 351ci_TotalFinancialAssetsAtFairValueExcludingSeparateAccounts
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 305ci_TotalFinancialAssetsAtFairValueExcludingSeparateAccounts
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Financial liabilities at fair value:    
Total financial liabilities at fair value 0us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 0us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Fair Value Inputs Level 1 [Member] | Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 0us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 0us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Financial liabilities at fair value:    
Derivative liabilities 0us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 0us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Fair Value Inputs Level 1 [Member] | Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 0us-gaap_DerivativeAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember		 0us-gaap_DerivativeAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember
Financial liabilities at fair value:    
Derivative liabilities 0us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember		 0us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember
Fair Value Inputs Level 1 [Member] | Federal government and agency [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 290us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		 297us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Fair Value Inputs Level 1 [Member] | State and local government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 0us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 0us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Fair Value Inputs Level 1 [Member] | Foreign government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 0us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember		 0us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
Fair Value Inputs Level 1 [Member] | Corporate [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 0us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 0us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Fair Value Inputs Level 1 [Member] | Mortgage-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 0us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember		 0us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
Fair Value Inputs Level 1 [Member] | Other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 0us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember		 0us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember
Fair Value Inputs Level 2 [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 17,879us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 15,058us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Equity securities 85us-gaap_MarketableSecuritiesEquitySecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 74us-gaap_MarketableSecuritiesEquitySecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Subtotal 17,964us-gaap_MarketableSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 15,132us-gaap_MarketableSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Short-term investments 163us-gaap_OtherShortTermInvestments
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 631us-gaap_OtherShortTermInvestments
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Total financial assets at fair value, excluding separate accounts 18,133ci_TotalFinancialAssetsAtFairValueExcludingSeparateAccounts
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 15,766ci_TotalFinancialAssetsAtFairValueExcludingSeparateAccounts
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Financial liabilities at fair value:    
Total financial liabilities at fair value 1us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 16us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Fair Value Inputs Level 2 [Member] | Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 6us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 3us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Financial liabilities at fair value:    
Derivative liabilities 1us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 16us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Fair Value Inputs Level 2 [Member] | Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 0us-gaap_DerivativeAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember		 0us-gaap_DerivativeAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember
Financial liabilities at fair value:    
Derivative liabilities 0us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember		 0us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember
Fair Value Inputs Level 2 [Member] | Federal government and agency [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 664us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		 583us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Fair Value Inputs Level 2 [Member] | State and local government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 1,856us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 2,144us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Fair Value Inputs Level 2 [Member] | Foreign government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 1,936us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember		 1,421us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
Fair Value Inputs Level 2 [Member] | Corporate [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 13,105us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 10,476us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Fair Value Inputs Level 2 [Member] | Mortgage-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 84us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember		 152us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
Fair Value Inputs Level 2 [Member] | Other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 234us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember		 282us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember
Fair Value Inputs Level 3 [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 814us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 1,131us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Equity securities 43us-gaap_MarketableSecuritiesEquitySecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 59us-gaap_MarketableSecuritiesEquitySecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Subtotal 857us-gaap_MarketableSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 1,190us-gaap_MarketableSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Short-term investments 0us-gaap_OtherShortTermInvestments
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 0us-gaap_OtherShortTermInvestments
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Total financial assets at fair value, excluding separate accounts 1,810ci_TotalFinancialAssetsAtFairValueExcludingSeparateAccounts
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 1,941ci_TotalFinancialAssetsAtFairValueExcludingSeparateAccounts
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Financial liabilities at fair value:    
Total financial liabilities at fair value 929us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 741us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Fair Value Inputs Level 3 [Member] | Run-off Settlement Annuity Business [Member] | Fair Value, Measurements, Recurring [Member]    
Financial liabilities at fair value:    
Net appreciation required to adjust future policy benefits for run-off settlement annuity business included in fixed maturities 65ci_UnrealizedAppreciationSettlementAnnuity
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_StatementBusinessSegmentsAxis
= ci_RunoffSettlementAnnuityBusinessMember		 60ci_UnrealizedAppreciationSettlementAnnuity
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_StatementBusinessSegmentsAxis
= ci_RunoffSettlementAnnuityBusinessMember
Fair Value Inputs Level 3 [Member] | Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 0us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 0us-gaap_DerivativeAssets
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Financial liabilities at fair value:    
Derivative liabilities 0us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember		 0us-gaap_DerivativeLiabilities
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_SwapMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
Fair Value Inputs Level 3 [Member] | Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Derivative assets 953us-gaap_DerivativeAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember		 751us-gaap_DerivativeAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember
Financial liabilities at fair value:    
Derivative liabilities 929us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember		 741us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_NetAmountAtRiskByProductAndGuaranteeGuaranteeTypeAxis
= us-gaap_GuaranteedMinimumIncomeBenefitMember
Fair Value Inputs Level 3 [Member] | Federal government and agency [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 0us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember		 0us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasuryAndGovernmentMember
Fair Value Inputs Level 3 [Member] | State and local government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 0us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 0us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Fair Value Inputs Level 3 [Member] | Foreign government [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 4us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember		 23us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ForeignGovernmentDebtSecuritiesMember
Fair Value Inputs Level 3 [Member] | Corporate [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 393us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 505us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Fair Value Inputs Level 3 [Member] | Mortgage-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities 1us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember		 1us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesMember
Fair Value Inputs Level 3 [Member] | Other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]    
Financial assets at fair value:    
Fixed maturities $ 416us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember		 $ 602us-gaap_MarketableSecuritiesFixedMaturities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsRecurringMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember
[1] Fixed maturities included $756 million of net appreciation required to adjust future policy benefits for the run-off settlement annuity business including $65 million of appreciation for securities classified in Level 3.
[2] Fixed maturities included $458 million of net appreciation required to adjust future policy benefits for the run-off settlement annuity business including $60 million of appreciation for securities classified in Level 3.
[3] Other derivative assets included $5 million of interest rate and foreign currency swaps qualifying as cash flow hedges and $1 million of interest rate swaps qualifying as fair value hedges. Other derivative liabilities reflected interest rate and foreign currency swaps qualifying as cash flow hedges. See Note 12 for additional information.
[4] Other derivative assets reflected interest rate and foreign currency swaps qualifying as cash flow hedges. Other derivative liabilities included $15 million of interest rate and foreign currency swaps qualifying as cash flow hedges and $1 million of interest rate and foreign currency swaps not designated as accounting hedges. See Note 12 for additional information.
[5] The GMIB assets represented retrocessional contracts in place from three external reinsurers that cover the exposures on these contracts.