Pension and Other Postretirement Employee Benefit Plans - Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Amortization:
Total net periodic defined benefit plan cost/(credit)	$ (59)	$ (72)
Total defined contribution plans	321	299
Total pension and OPEB cost included in noninterest expense	262	227
Pension plans | U.S.
Components of net periodic benefit cost, U.S. defined benefit pension plans
Benefits earned during the period	0	0
Interest cost on benefit obligations	85	105
Expected return on plan assets	(129)	(158)
Amortization:
Net (gain)/loss	3	2
Prior service (credit)/cost	0	0
Net periodic defined benefit plan cost/(credit), U.S. defined benefit pension plans	(41)	(51)
OPEB plans
Amortization:
Other defined benefit pension and OPEB plans	$ (18)	$ (21)