Leases - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Property leases
Cash payments for lease liabilities within operating activities:
Operating leases	$ 963	$ 947	$ 838
Non-cash activities - increase in right-of-use assets in exchange for lease liabilities:
Operating leases	1,086	1,404	1,079
Buses and support vehicles
Cash payments for lease liabilities within operating activities:
Operating leases	119	151	167
Vehicle finance leases	6	7	6
Cash payments for lease liabilities within financing activities:
Vehicle finance leases	103	105	105
Non-cash activities - increase in right-of-use assets in exchange for lease liabilities:
Operating leases	81	112	191
Vehicle finance leases	$ 74	$ 102	$ 118