Details of Intangible Assets Included in Other Long-Term Assets (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	9 years 9 months 18 days
Cost	$ 753	$ 753
Accumulated Amortization	417	396
Net	$ 336	357
Customer contracts/ relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	9 years 9 months 18 days
Cost	$ 566	566
Accumulated Amortization	307	292
Net	$ 259	274
Trade names and technology
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	8 years 3 months 18 days
Cost	$ 104	104
Accumulated Amortization	58	54
Net	$ 46	50
Provider contracts
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	14 years 7 months 6 days
Cost	$ 51	51
Accumulated Amortization	25	24
Net	$ 26	27
Noncompetes and other
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	8 years 2 months 12 days
Cost	$ 32	32
Accumulated Amortization	27	26
Net	$ 5	$ 6