Leases - Summary of remaining operating lease payments (Detail) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Operating Lease Liabilities, Payments Due [Abstract]
2019	$ 599
2019		$ 1,310
2020	1,346	1,268
2021	1,123	1,048
2022	885	820
2023	708	658
Thereafter	2,289	2,079
Total lease payments	6,950	$ 7,183
Amount representing interest	(1,016)
Lease liabilities	$ 5,934