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SEGMENT INFORMATION - Additional Information (Detail) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2017 USD ($) | Jun. 30, 2016 USD ($) | Jun. 30, 2017 USD ($) Segment | Jun. 30, 2016 USD ($)
Segment Reporting [Abstract] |  |  |  |
Number of reportable segments | Segment |  |  | 4 |
Member co-share amounts and government subsidies | $ 3,200 | $ 3,200 | $ 6,200 | $ 6,200
Depreciation and amortization classified as benefit expense | $ 27 | $ 27 | $ 53 | $ 54

X
- Definition Depreciation and amortization expense that has been reclassified to be included with benefit expenses. The reclassification is the result of depreciation and amortization expense associated primarily from the delivery of pharmacy services by our wholly-owned pharmacy business included in our Healthcare Services segment. + References No definition available. + Details
Name: | hum_DepreciationAndAmortizationClassifiedAsBenefitExpense
Namespace Prefix: | hum_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of member co-share amounts and government subsidies that are excluded from benefits expense because the health plans do not bear responsibility. + References No definition available. + Details
Name: | hum_GovernmentAndHealthPlanMemberSubsidiesAmount
Namespace Prefix: | hum_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. + References No definition available. + Details
Name: | us-gaap_NumberOfReportableSegments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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