Pension and Other Postretirement Employee Benefit Plans - Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension and OPEB plans
Total net periodic defined benefit plan cost/(credit)	$ (201)	$ (285)	$ 144
Total defined contribution plans	1,333	1,332	952
Total pension and OPEB cost included in noninterest expense	1,132	1,047	1,096
Total recognized in other comprehensive income	$ (1,129)	$ (214)	$ (1,157)
Weighted-average assumptions used to determine net periodic benefit costs
Discount rate	2.17%	2.93%	3.89%
Expected long-term rate of return on plan assets	2.97%	3.91%	5.08%