Changes In Carrying Amount Of Goodwill By Reportable Segments (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Goodwill [Line Items]
Balance at January 1, 2012	$ 2,740
Acquisitions	222
Balance at September 30, 2012	2,962
Retail
Goodwill [Line Items]
Balance at January 1, 2012	754
Acquisitions	46
Balance at September 30, 2012	800
Employer Group
Goodwill [Line Items]
Balance at January 1, 2012	62
Acquisitions	0
Balance at September 30, 2012	62
Health And Well-Being Services
Goodwill [Line Items]
Balance at January 1, 2012	1,867
Acquisitions	136
Balance at September 30, 2012	2,003
Other Businesses
Goodwill [Line Items]
Balance at January 1, 2012	57
Acquisitions	40
Balance at September 30, 2012	$ 97