Benefits Payable (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Benefits Payable [Abstract]
Prior year favorable reserve releases	$ 205	$ 231
Military services benefits payable	$ 339	$ 255

Prior year favorable reserve releases not in the ordinary course of business

No definition available.

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