Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Loss Contingencies [Line Items]
Rental expense under operating lease agreements	$ 367	$ 291	$ 1,000	$ 824
Capital Lease Obligations, Current	3,700		3,700		$ 3,000
Finance Lease Obligations, Current	135		135		99
Capital Lease Obligations, Noncurrent	4,500		4,500		4,200
Finance Lease Obligations, Noncurrent	2,400		2,400		1,700
Tax contingencies	1,700		1,700		1,200
Pledged Assets	$ 588		$ 588		$ 418