Special Charges - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Restructuring Cost and Reserve [Line Items]
Labor contract ratification bonuses	$ 1	$ 0	$ 814	$ 0
(Gains) losses on sale of assets and other special charges	28	20	88	124
Nonoperating unrealized (gains) losses	$ 54	(28)	(54)	12
Deferred debt issuance cost, writeoff			11	7
Loss contingency, loss in period		94		94
Unsecured Debt
Restructuring Cost and Reserve [Line Items]
Repayments of debt			$ 1,000
Long-term debt		$ 400		$ 400
Stated interest rate		4.25%		4.25%