v3.8.0.1

Medical Claims Liability - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Insurance [Abstract] |  |  |
Amounts recorded as an adjustment to premium revenues related to minimum HBR and return of premium programs | $ 1 | $ 39 | $ 47

X
- Definition Amounts recorded as a reduction to premium revenues related to minimum HBR and return of premium programs + References No definition available. + Details
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Namespace Prefix: | cnc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_InsuranceAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration