Pension and Other Postretirement Employee Benefit Plans - Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension and OPEB plans
Total net periodic defined benefit plan cost/(credit)	$ (393)	$ (192)	$ (201)
Total defined contribution plans	1,609	1,408	1,333
Total pension and OPEB cost included in noninterest expense	1,216	1,216	1,132
Total recognized in other comprehensive (income)/loss	$ (421)	1,459	(1,129)
Defined benefit pension plans
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss		$ 92	$ 33