SEGMENT INFORMATION - Narrative (Details) $ in Millions	3 Months Ended
Mar. 31, 2019 USD ($) Segment	Mar. 31, 2018 USD ($)
Segment Reporting [Abstract]
Number of reportable segments \| Segment	3
Member co-share amounts and government subsidies	$ 3,100	$ 2,900
Depreciation and amortization classified as benefit expense	$ 29	$ 39

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.

No definition available.

Name:	hum_DepreciationAndAmortizationClassifiedAsBenefitExpense
Namespace Prefix:	hum_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration