Details of Intangible Assets Included in Other Long-Term Assets (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	9 years 10 months 24 days
Cost	$ 755	$ 865
Accumulated Amortization	376	425
Net	$ 379	440
Customer contracts/ relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	9 years 10 months 24 days
Cost	$ 567	657
Accumulated Amortization	278	326
Net	$ 289	331
Trade names and technology
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	8 years 2 months 12 days
Cost	$ 105	115
Accumulated Amortization	50	50
Net	$ 55	65
Provider contracts
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	14 years 7 months 6 days
Cost	$ 51	52
Accumulated Amortization	23	21
Net	$ 28	31
Noncompetes and other
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	8 years 2 months 12 days
Cost	$ 32	41
Accumulated Amortization	25	28
Net	$ 7	$ 13