Pension and Other Postretirement Employee Benefit Plans - Fair Value Measurement of the Plans' Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 19,890	$ 25,692
Total fair value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17,538	22,028
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,308	6,541
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9,617	12,315
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,613	3,172
Assets measured at fair value using net asset value per share as practical expedient
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,593	3,960
Defined benefit pension plans
Defined Benefit Plan Disclosure [Line Items]
Net defined benefit pension plan payables not classified in fair value hierarchy	$ (241)	$ (296)