Leases - Summary of remaining operating lease payments (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Operating Lease Liabilities, Payments Due [Abstract]
2019	$ 296
2019		$ 1,310
2020	1,363	1,268
2021	1,140	1,048
2022	915	820
2023	732	658
Thereafter	2,423	2,079
Total lease payments	6,869	$ 7,183
Amount representing interest	(1,017)
Lease liabilities	$ 5,852