Pension Plans and Other Postretirement Benefits - Net Periodic Benefit Cost (Income) (Details) - Pension Plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Components of net periodic benefit cost (income):
Interest cost	$ 231	$ 132	$ 110
Expected return on plan assets	(326)	(309)	(317)
Amortization of net actuarial loss	1	3	5
Settlement losses	0	1	16
Net periodic benefit cost (income)	$ (94)	$ (173)	$ (186)