Leases and Capacity Purchase Agreements - Summary of Scheduled Future Minimum Lease Payments under Operating and Finance Leases (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Operating Leases
2024	$ 813
2025	726
2026	706
2027	885
2028	685
After 2028	2,942
Minimum lease payments	6,757
Imputed interest	(1,678)
Present value of minimum lease payments	5,079
Less: current maturities of lease obligations	(576)	$ (561)
Long-term lease obligations	4,503	4,459
Finance Leases
2024	183
2025	60
2026	19
2027	9
2028	8
After 2028	5
Minimum lease payments	284
Imputed interest	(21)
Present value of minimum lease payments	263
Less: current maturities of lease obligations	(172)	(104)
Long-term lease obligations	$ 91	$ 115