Employee Benefits - Unfunded Status (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Non-current portion of unfunded status	$ (2,391)	$ (3,710)
Combined Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	(5,295)	(9,678)	$ (12,202)	$ (12,217)
Fair value of plan assets (liabilities)	4,715	8,531	10,546	10,493
Unfunded status	(580)	(1,147)
Current portion of unfunded status	0	0
Non-current portion of unfunded status	(580)	(1,147)
Post-Retirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	(1,995)	(2,781)	(3,048)	$ (3,037)
Fair value of plan assets (liabilities)	5	5	$ 5
Unfunded status	(1,990)	(2,776)
Current portion of unfunded status	(210)	(212)
Non-current portion of unfunded status	$ (1,780)	$ (2,564)