Acquisitions, Disposals and Other Transactions - Schedule of Total Transaction Value/ Fair Value of Acquisition (Detail) - 1 months ended Sep. 30, 2016 - Wireless Group plc [Member] £ in Millions, $ in Millions	USD ($)	GBP (£)
Business Acquisition [Line Items]
Cash paid for Wireless Group equity	$ 285	£ 220
Plus: Assumed debt	23
Total transaction value	$ 308