Pension and Other Postretirement Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		$ 204	$ 239	$ 216
Interest cost		188	184	209
Expected return on plan assets		(306)	(283)	(328)
Amortization of unrecognized actuarial (gain) loss		120	170	162
Amortization of prior service credits		0	0	0
Settlement loss - Voluntary Programs		0	0	430
Special termination benefits - Voluntary Programs		0	0	54
Curtailment		0	(8)	1
Other		5	5	22
Net periodic benefit cost (credit)		211	307	766
Pension Benefits | Forecast
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost (credit)	$ 97
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		9	10	10
Interest cost		30	25	28
Expected return on plan assets		(1)	(1)	(1)
Amortization of unrecognized actuarial (gain) loss		(14)	(28)	(40)
Amortization of prior service credits		(112)	(123)	(124)
Settlement loss - Voluntary Programs		0	0	0
Special termination benefits - Voluntary Programs		0	31	201
Curtailment		0	0	0
Other		0	0	0
Net periodic benefit cost (credit)		$ (88)	$ (86)	$ 74
Other Postretirement Benefits | Forecast
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost (credit)	$ (105)