Employee Benefits - Unfunded Status (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Non-current portion of unfunded status	$ (2,205)	$ (2,490)
Combined Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	(4,816)	(5,212)	$ (5,295)	$ (9,678)
Fair value of plan assets (liabilities)	4,201	4,476	4,715	8,531
Unfunded status	(615)	(736)
Current portion of unfunded status	0	0
Non-current portion of unfunded status	(615)	(736)
Post-Retirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	(1,750)	(1,919)	(1,995)	$ (2,781)
Fair value of plan assets (liabilities)	1	1	$ 5
Unfunded status	(1,749)	(1,918)
Current portion of unfunded status	(186)	(193)
Non-current portion of unfunded status	$ (1,563)	$ (1,725)