Employee Benefit Plans - Benefit Obligations, Fair Value of Plan Assets and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Change in Benefit Obligation
Benefit obligation at beginning of period	$ 22,626	$ 21,199
Service cost	0	0	$ 0
Interest cost	582	700	833
Actuarial (gain)/loss	(851)	2,051
Benefits paid, including lump sums and annuities	(1,279)	(1,233)
Participant contributions	0	0
Special termination benefits	0	0
Settlements	(5)	(91)
Benefit obligation at end of period	21,073	22,626	21,199
Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of period	16,541	15,845
Actual gain on plan assets	2,732	1,973
Employer contributions	1,513	47
Participant contributions	0	0
Benefits paid, including lump sums and annuities	(1,279)	(1,233)
Settlements	(5)	(91)
Fair value of plan assets at end of period	19,502	16,541	15,845
Funded Status of Plan
Funded status at end of period	(1,571)	(6,085)
Other Postretirement and Postemployment Benefits
Change in Benefit Obligation
Benefit obligation at beginning of period	4,766	3,379
Service cost	86	96	83
Interest cost	117	120	137
Actuarial (gain)/loss	23	247
Benefits paid, including lump sums and annuities	(405)	(356)
Participant contributions	18	20
Special termination benefits	0	1,260
Settlements	0	0
Benefit obligation at end of period	4,605	4,766	3,379
Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of period	496	607
Actual gain on plan assets	57	76
Employer contributions	192	189
Participant contributions	18	20
Benefits paid, including lump sums and annuities	(406)	(396)
Settlements	0	0
Fair value of plan assets at end of period	357	496	$ 607
Funded Status of Plan
Funded status at end of period	$ (4,248)	$ (4,270)