Changes in Carrying Amount of Goodwill by Reportable Segments (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2014
Goodwill [Line Items]
Beginning Balance	$ 3,733
Acquisitions	3
Dispositions	(40)
Subsequent payments/adjustments	(1)
Ending Balance	3,695
Retail
Goodwill [Line Items]
Beginning Balance	1,007
Acquisitions	0
Dispositions	0
Subsequent payments/adjustments	0
Ending Balance	1,007
Employer Group
Goodwill [Line Items]
Beginning Balance	363
Acquisitions	0
Dispositions	0
Subsequent payments/adjustments	0
Ending Balance	363
Healthcare Services
Goodwill [Line Items]
Beginning Balance	2,271
Acquisitions	3
Dispositions	(40)
Subsequent payments/adjustments	(1)
Ending Balance	2,233
Other Businesses
Goodwill [Line Items]
Beginning Balance	92
Acquisitions	0
Dispositions	0
Subsequent payments/adjustments	0
Ending Balance	$ 92

Goodwill, Subsequent Payments And Adjustments

No definition available.

Name:	hum_GoodwillSubsequentPaymentsAndAdjustments
Namespace Prefix:	hum_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

+ Details

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

+ Details

Name:	us-gaap_GoodwillAcquiredDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_GoodwillLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

+ Details

Name:	us-gaap_GoodwillWrittenOffRelatedToSaleOfBusinessUnit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration