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Segment Information - Concentration Risk (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Concentration Risk [Line Items]      
Premiums, accounts and notes receivable, net 3,309us-gaap_PremiumsAndOtherReceivablesNet   $ 2,757us-gaap_PremiumsAndOtherReceivablesNet
Government Contracts Concentration Risk [Member] | CMS [Member]      
Concentration Risk [Line Items]      
Premiums, accounts and notes receivable, net 1,100us-gaap_PremiumsAndOtherReceivablesNet
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_GovernmentContractsConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= ci_CentersForMedicareAndMedicaidServicesMember		   $ 800us-gaap_PremiumsAndOtherReceivablesNet
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_GovernmentContractsConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= ci_CentersForMedicareAndMedicaidServicesMember
Revenue Consolidated [Member] | Government Contracts Concentration Risk [Member] | CMS [Member]      
Concentration Risk [Line Items]      
Concentration percentage 22.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= ci_RevenueConsolidatedMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_GovernmentContractsConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= ci_CentersForMedicareAndMedicaidServicesMember		 22.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= ci_RevenueConsolidatedMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_GovernmentContractsConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= ci_CentersForMedicareAndMedicaidServicesMember