v2.4.1.9

Short-Term And Long-Term Investments And Restricted Deposits (Contractual Maturities Of Short-Term And Long-Term Investments And Restricted Deposits) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Investments [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
One year or less, Amortized Cost | $ 176 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesWithinOneYearAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember | $ 102 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesWithinOneYearAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember
One year through five years, Amortized Cost | 1,121 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterOneThroughFiveYearsAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember | 610 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterOneThroughFiveYearsAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember
Five years through ten years, Amortized Cost | 121 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterFiveThroughTenYearsAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember | 157 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterFiveThroughTenYearsAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember
Greater than ten years, Amortized Cost | 38 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterTenYearsAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember | 30 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterTenYearsAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember
Total, Amortized Cost | 1,456 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember | 899 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember
One year or less, Fair Value | 177 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesWithinOneYearFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember | 102 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesWithinOneYearFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember
One year through five years, Fair Value | 1,121 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterOneThroughFiveYearsFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember | 611 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterOneThroughFiveYearsFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember
Five years through ten years, Fair Value | 120 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterFiveThroughTenYearsFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember | 151 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterFiveThroughTenYearsFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember
Greater than ten years, Fair Value | 39 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterTenYearsFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember | 30 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterTenYearsFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember
Total, Fair Value | 1,457 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember | 894 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_InvestmentsMember
Restricted Deposits [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
One year or less, Amortized Cost | 92 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesWithinOneYearAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember | 41 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesWithinOneYearAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember
One year through five years, Amortized Cost | 8 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterOneThroughFiveYearsAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember | 6 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterOneThroughFiveYearsAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember
Five years through ten years, Amortized Cost | 0 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterFiveThroughTenYearsAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember | 0 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterFiveThroughTenYearsAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember
Greater than ten years, Amortized Cost | 0 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterTenYearsAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember | 0 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterTenYearsAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember
Total, Amortized Cost | 100 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember | 47 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAmortizedCost / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember
One year or less, Fair Value | 92 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesWithinOneYearFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember | 41 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesWithinOneYearFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember
One year through five years, Fair Value | 8 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterOneThroughFiveYearsFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember | 6 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterOneThroughFiveYearsFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember
Five years through ten years, Fair Value | 0 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterFiveThroughTenYearsFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember | 0 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterFiveThroughTenYearsFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember
Greater than ten years, Fair Value | 0 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterTenYearsFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember | 0 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesAfterTenYearsFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember
Total, Fair Value | $ 100 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember | $ 47 cnc_InvestmentsAndRestrictedDepositsContractualMaturitiesFairValue / cnc_ScheduleOfContractualMaturitiesOfInvestmentsAndRestrictedDepositsAxis = us-gaap_DepositsMember

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