Property and Equipment - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Significant Acquisitions and Disposals [Line Items]
Internal-use software	$ 1,300,000,000	$ 1,100,000,000
Depreciation expense	3,616,000,000	2,460,000,000	1,653,000,000
Amortization of property and equipment acquired under capital leases	1,500,000,000	826,000,000	510,000,000
Gross assets remaining under capital leases	7,900,000,000	4,200,000,000
Accumulated depreciation associated with capital leases	3,300,000,000	1,900,000,000
Gross assets remaining under finance leases	1,400,000,000	578,000,000
Accumulated depreciation associated with finance leases	87,000,000	22,000,000
Cash paid For interest on capital and finance leases	$ 86,000,000	$ 41,000,000	$ 51,000,000