Acquisitions - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended	1 Months Ended	3 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jul. 06, 2012 Senior Bridge Family Companies Inc	Jun. 30, 2013 Metropolitan Health Networks, Inc.	Jun. 30, 2013 Arcadian Management Services Inc State	Jun. 30, 2013 MCCI Holdings LLC
Business Acquisition [Line Items]
Estimated transaction value to acquire the entity				$ 851
Date of acquisition			Jul. 06, 2012	Dec. 21, 2012	Mar. 31, 2012	Oct. 29, 2012
Excess of consideration over estimated fair value of net tangible assets acquired				833
Amount allocated to other intangible assets			14	263	38
Goodwill acquired			99	570	44
Other intangible assets useful life, years	10 years 4 months 24 days		5 years 2 months 12 days	8 years 4 months 24 days	9 years 8 months 12 days
Arcadian Member States					15
Acquisition-related costs		$ 27