Leases and Capacity Purchase Agreements - Summary of Scheduled Future Minimum Lease Payments under Operating and Finance Leases (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Operating Leases
2022	$ 857
2023	825
2024	775
2025	655
2026	637
After 2026	3,982
Minimum lease payments	7,731
Imputed interest	(2,023)
Present value of minimum lease payments	5,708
Less: current maturities of lease obligations	(556)	$ (612)
Long-term lease obligations	5,152	4,986
Finance Leases
2022	89
2023	57
2024	53
2025	41
2026	26
After 2026	72
Minimum lease payments	338
Imputed interest	(43)
Present value of minimum lease payments	295
Less: current maturities of lease obligations	(76)	(182)
Long-term lease obligations	$ 219	$ 224