Leases - Components of operating lease costs (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Lease Cost [Abstract]
Operating lease cost	$ 367	$ 728
Short-term lease cost	35	79
Variable lease cost	70	139
Sublease income	(6)	(12)
Total lease cost	$ 466	$ 934