Pension and Other Postretirement Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 239	$ 216	$ 184
Interest cost	184	209	226
Expected return on plan assets	(283)	(328)	(291)
Amortization of unrecognized actuarial (gain) loss	170	162	118
Amortization of prior service credits	0	0	0
Settlement loss - Voluntary Programs	0	430	0
Special termination benefit - Voluntary Programs	0	54	0
Curtailment	(8)	1	0
Other	5	22	5
Net periodic benefit cost (credit)	307	766	242
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	10	10	10
Interest cost	25	28	47
Expected return on plan assets	(1)	(1)	(1)
Amortization of unrecognized actuarial (gain) loss	(28)	(40)	(52)
Amortization of prior service credits	(123)	(124)	(73)
Settlement loss - Voluntary Programs	0	0	0
Special termination benefit - Voluntary Programs	31	201	0
Curtailment	0	0	0
Other	0	0	0
Net periodic benefit cost (credit)	$ (86)	$ 74	$ (69)