Special Charges (Credits) - Components of Special Charges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating:
Labor contract ratification bonuses	$ 814	$ 0	$ 0
CARES Act grant	0	0	(4,021)
Severance and benefit costs	0	0	438
Impairment of assets	0	0	97
(Gains) losses on sale of assets and other special charges	135	140	119
Total operating special charges (credits)	949	140	(3,367)
Nonoperating unrealized (gains) losses on investments, net	(27)	(20)	34
Nonoperating debt extinguishment and modification fees	11	7	50
Nonoperating special termination benefits and settlement losses	0	0	31
Total nonoperating special charges and unrealized (gains) losses on investments, net	(16)	(13)	115
Total operating and nonoperating special charges (credits) and unrealized (gains) losses on investments, net	933	127	(3,252)
Income tax expense (benefit), net of valuation allowance	(214)	(33)	728
Total operating and nonoperating special charges (credits) and unrealized (gains) losses on investments, net of income taxes	$ 719	$ 94	$ (2,524)