Acquisitions - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) Acquisition	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Goodwill	$ 296	$ 346
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Number of acquisitions completed | Acquisition	6
Purchase price	$ 431
Goodwill	221
Intangible assets	84
Business Acquisition Acquiree One
Business Acquisition [Line Items]
Business acquisition, maximum contingent consideration payments	6
Business acquisition, fair value of contingent consideration payments as of acquisition date	$ 4