Acquisitions - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended		9 Months Ended	1 Months Ended	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 American Eldercare Inc.	Jul. 06, 2012 Senior Bridge Family Companies Inc	Sep. 30, 2013 Metropolitan Health Networks, Inc.	Sep. 30, 2013 Arcadian Management Services Inc State	Sep. 30, 2013 MCCI Holdings LLC
Business Acquisition [Line Items]
Date of acquisition			Sep. 06, 2013	Jul. 06, 2012	Dec. 21, 2012	Mar. 31, 2012	Oct. 29, 2012
Goodwill acquired	$ 3,716	$ 3,640	$ 75	$ 99	$ 570	$ 44
Amount allocated to other intangible assets			75	14	263	38
Other intangible assets useful life, years	10 years 3 months 18 days		9 years 3 months 18 days	5 years 2 months 12 days	8 years 4 months 24 days	9 years 8 months 12 days
Estimated transaction value to acquire the entity					851
Excess of consideration over estimated fair value of net tangible assets acquired					$ 833
Arcadian Member States						15