Pension and Other Postretirement Employee Benefit Plans - Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Amortization:
Total net periodic defined benefit plan cost/(credit)	$ (60)	$ (72)	$ (119)	$ (144)
Total defined contribution plans	350	321	671	620
Total pension and OPEB cost included in noninterest expense	290	249	552	476
Pension plans | U.S.
Components of net periodic benefit cost, U.S. defined benefit pension plans
Benefits earned during the period	1	1	1	1
Interest cost on benefit obligations	86	106	171	211
Expected return on plan assets	(129)	(159)	(258)	(317)
Amortization:
Net (gain)/loss	2	1	5	3
Net periodic defined benefit plan cost/(credit), U.S. defined benefit pension plans	(40)	(51)	(81)	(102)
OPEB plans
Amortization:
Other defined benefit pension and OPEB plans	$ (20)	$ (21)	$ (38)	$ (42)