Benefit Plans - Components of net periodic cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Components of net periodic cost
Service cost	$ 104	$ 108	$ 125
Interest cost	199	221	254
Expected return on plan assets	(445)	(414)	(403)
Amortization of prior service credit	(75)	(64)	(59)
Curtailment losses (gains)	0	2	0
Costs and expenses	(217)	(147)	(83)
Remeasurement of projected benefit obligation	(325)	835	946
Remeasurement of plan assets	(319)	(886)	(832)
Remeasurement (gains) losses	(644)	(51)	114
Total net (benefit) cost	(861)	(198)	31
Pension benefits
Components of net periodic cost
Service cost	103	104	117
Interest cost	191	210	240
Expected return on plan assets	(445)	(414)	(403)
Amortization of prior service credit	(50)	(54)	(56)
Curtailment losses (gains)	0	10	0
Costs and expenses	(201)	(144)	(102)
Remeasurement of projected benefit obligation	(309)	813	927
Remeasurement of plan assets	(319)	(886)	(832)
Remeasurement (gains) losses	(628)	(73)	95
Total net (benefit) cost	(829)	(217)	(7)
Postretirement benefits
Components of net periodic cost
Service cost	1	4	8
Interest cost	8	11	14
Expected return on plan assets	0	0	0
Amortization of prior service credit	(25)	(10)	(3)
Curtailment losses (gains)	0	(8)	0
Costs and expenses	(16)	(3)	19
Remeasurement of projected benefit obligation	(16)	22	19
Remeasurement of plan assets	0	0	0
Remeasurement (gains) losses	(16)	22	19
Total net (benefit) cost	$ (32)	$ 19	$ 38