Leases - Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Supplemental Balance Sheet Information Related to Leases [Line Items]
Operating lease ROU assets	$ 2,405	$ 2,368
Short-term operating lease liabilities	555	496
Long-term operating lease liabilities	$ 1,884	$ 1,910
Weighted average discount rate	1.82%	1.25%
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Accounts Payable and Accrued Liabilities, Current	Accounts Payable and Accrued Liabilities, Current
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Vehicles, net	Vehicles, net
Finance Lease, Liability, Statement of Financial Position [Extensible Enumeration]	Total	Total
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Operating lease ROU assets	Operating lease ROU assets
Operating Lease, Liability, Statement of Financial Position [Extensible Enumeration]	Operating lease ROU assets	Operating lease ROU assets
Property
Supplemental Balance Sheet Information Related to Leases [Line Items]
Operating lease ROU assets	$ 2,405	$ 2,368
Short-term operating lease liabilities	555	496
Long-term operating lease liabilities	1,884	1,910
Operating lease liabilities	$ 2,439	$ 2,406
Weighted average remaining lease term	8 years 2 months 12 days	8 years 9 months 18 days
Weighted average discount rate	4.30%	3.84%
Buses and support vehicles
Supplemental Balance Sheet Information Related to Leases [Line Items]
Operating lease ROU assets	$ 86	$ 63
Short-term operating lease liabilities	64	50
Long-term operating lease liabilities	22	14
Operating lease liabilities	$ 86	$ 64
Weighted average remaining lease term	1 year 4 months 24 days	1 year 3 months 18 days
Weighted average discount rate	4.86%	2.66%
Finance lease ROU assets, gross	$ 267	$ 353
Accumulated amortization	(45)	(72)
Finance Lease ROU assets, net	222	281
Short-term vehicle finance lease liabilities	44	126
Long-term vehicle finance lease liabilities	132	116
Total	$ 176	$ 242
Weighted average remaining lease term	2 years	2 years 2 months 12 days
Weighted average discount rate	1.82%	1.97%