Fair Value Measurements - Fair Value Assets and Liabilities Measured on Recurring Basis with Unobservable Inputs (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2024
Fuel derivative contracts
Total gains (losses) for the period
Purchases	$ 16	$ 67
Fuel derivative contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	257	223
Total gains (losses) for the period
Included in earnings	(2)	(3)
Included in other comprehensive income	(30)	(29)
Settlements	(21)	(38)
Ending Balance	220	220
The amount of total losses for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held as of June 30, 2024	2	2
The amount of total losses for the period included in other comprehensive income attributable to the change in unrealized gains or losses relating to assets still held as of June 30, 2024	$ 23	$ 35