Segment and Related Information - Summary of Property and Equipment (Net) Relating to Operations by Segment (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	$ 10,665	$ 10,657	$ 12,344
United States and Puerto Rico [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	9,778	9,586	11,198
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	$ 887	$ 1,071	$ 1,146