Pension and Other Postretirement Employee Benefit Plans - Net Periodic Benefit Costs and Fair Value of Plan Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Retirement Benefits [Abstract]
Total net periodic defined benefit plan cost/(credit)	$ (64)	$ (59)
Total defined contribution plans	344	321
Total pension and OPEB cost included in noninterest expense	$ 280	$ 262