Pension and Other Postretirement Employee Benefit Plans - Net Periodic Benefit Costs and Fair Value of Plan Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Retirement Benefits [Abstract]
Total net periodic defined benefit plan cost/(credit)	$ (104)	$ (11)	$ (292)	$ (150)
Total defined contribution plans	403	353	1,165	1,054
Total pension and OPEB cost included in noninterest expense	$ 299	342	$ 873	904
Pension
Defined Benefit Plan Disclosure [Line Items]
Settlement loss		$ 58		$ 58