Rent Expense and Sublease Rental Income Associated With Operating Leases (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2010
Commitments and Contingencies Disclosure [Abstract]
Rent expense	$ 226us-gaap_LeaseAndRentalExpense	$ 227us-gaap_LeaseAndRentalExpense	$ 218us-gaap_LeaseAndRentalExpense
Sublease rental income	(14)	(11)	(11)
Net rent expense	$ 212hum_OperatingLeaseRentalExpensesNet	$ 216hum_OperatingLeaseRentalExpensesNet	$ 207hum_OperatingLeaseRentalExpensesNet

The amount of revenue recognized for the period under subleasing arrangements.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 55

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6584307&loc=d3e41620-112719

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