Segment and Related Information - Geographical (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Geographical
Operating revenues	$ 20,426	$ 19,698	$ 17,931
Property and equipment, net	16,968	15,719
U.S.
Geographical
Operating revenues	19,595	18,860	17,136
Property and equipment, net	15,903	14,721
Canada
Geographical
Operating revenues	813	838	$ 795
Property and equipment, net	1,060	994
Other
Geographical
Operating revenues	18
Property and equipment, net	$ 5	$ 4