Comprehensive Income (Loss) - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil		$ 5,975	$ 3,310	$ 1,849
Other (gains) losses, net		12	(50)	158
Less: Tax expense		189	348	(1,182)
Net income (loss)	$ (220)	539	977	(3,074)
Other operating expenses		3,735	$ 2,394	$ 1,926
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)		(634)
Defined benefit plan items | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (gains) losses, net		(2)
Less: Tax expense		0
Net income (loss)		(2)
Fuel derivative contracts | Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil		(832)
Other (gains) losses, net		0
Less: Tax expense		(195)
Net income (loss)		(637)
Interest rate derivatives | Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Less: Tax expense		2
Net income (loss)		5
Other operating expenses		$ 7