Segment Information - Additional Information (Detail) (USD $)	3 Months Ended
Mar. 31, 2015 Segment	Mar. 31, 2014
Segment Reporting [Abstract]
Number of reportable segments	3us-gaap_NumberOfReportableSegments
Member co-share amounts and government subsidies	$ 2,500,000,000	$ 1,900,000,000
Depreciation and amortization classified as benefit expense	$ 21,000,000	$ 25,000,000

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