Acquisitions - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended	0 Months Ended		1 Months Ended	0 Months Ended
	Dec. 31, 2014	Sep. 06, 2013	Dec. 21, 2012	Jul. 06, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012
Business Acquisition [Line Items]
Goodwill acquired	$ 3,711					$ 3,733	$ 3,640
Other intangible assets useful life, years	10 years 5 months 24 days
American Eldercare Inc.
Business Acquisition [Line Items]
Goodwill acquired		76
Amount allocated to other intangible assets		75
Other intangible assets useful life, years		9 years 3 months 18 days
Metropolitan Health Networks, Inc.
Business Acquisition [Line Items]
Goodwill acquired			564
Amount allocated to other intangible assets			263
Other intangible assets useful life, years			8 years 4 months 24 days
Estimated transaction value to acquire the entity			851
Excess of consideration over estimated fair value of net tangible assets acquired			827
Senior Bridge Family Companies Inc
Business Acquisition [Line Items]
Goodwill acquired				99
Amount allocated to other intangible assets				14
Other intangible assets useful life, years				5 years 2 months 12 days
Arcadian Management Services Inc
Business Acquisition [Line Items]
Goodwill acquired					44
Amount allocated to other intangible assets					$ 38
Other intangible assets useful life, years					9 years 8 months 12 days
Arcadian Member States					15