Segment and Related Information - Summary of Property and Equipment (Net) Relating to Operations by Segment (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	$ 10,657	$ 12,344	$ 12,651
United States and Puerto Rico [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	9,586	11,198	11,293
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	$ 1,071	$ 1,146	$ 1,358