Commitments and contingencies - Narrative (Details)	Jun. 30, 2021 USD ($) aircraft agreement
Other Commitments [Line Items]
Number of supplemental agreements | agreement	3
Number of firm orders	34
Firm orders exercised	2
Firm orders to be exercised in the future	32
Aircrafts to be purchased	660
MAX 7 Firm Orders
Other Commitments [Line Items]
Aircrafts to be purchased	234
MAX 7 or 8 Options
Other Commitments [Line Items]
Aircrafts to be purchased	268
LAX Terminal 1.5
Other Commitments [Line Items]
Total Not to Exceed Cost Of Airport Project | $	$ 410,000,000
Construction obligation | $	365,000,000
Dallas Love Field Terminal
Other Commitments [Line Items]
Municipal bonds principal remaining | $	399,000,000
Net present value of principal remaining | $	$ 432,000,000
Order Options Accelerated Into 2022
Other Commitments [Line Items]
Aircraft orders accelerated	10
Order Options Accelerated Into 2023
Other Commitments [Line Items]
Aircraft orders accelerated	32
Order Options Accelerated Into 2024
Other Commitments [Line Items]
Aircraft orders accelerated	16
Order Options Accelerated Into 2025
Other Commitments [Line Items]
Aircraft orders accelerated	16
Order Options Accelerated Into 2026 And 2027
Other Commitments [Line Items]
Aircraft orders accelerated	32
Other Commitments, Firm and Option Aircraft Orders | MAX 7 Firm Orders
Other Commitments [Line Items]
Aircrafts to be purchased	660
Cash Capital Commitments, Boeing Orders
Other Commitments [Line Items]
Remainder of 2021 | $	$ 0
2022 | $	1,500,000,000
2023 | $	1,200,000,000
2024 | $	1,100,000,000
2025 | $	835,000,000
2026 | $	971,000,000
Thereafter | $	$ 7,000,000,000.0