Borrowed Funds (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Borrowed funds	$ 72,707	$ 72,737
Parent Company
Debt Instrument [Line Items]
Borrowed funds	25,039	23,971
Parent Company | Senior debt
Debt Instrument [Line Items]
Borrowed funds	23,303	22,221
Basis adjustments - Fair value accounting hedges	(724)
Parent Company | Subordinated debt
Debt Instrument [Line Items]
Borrowed funds	1,530	1,544
Basis adjustments - Fair value accounting hedges	(66)
Subsidiaries
Debt Instrument [Line Items]
Borrowed funds	44,695	45,740
Subsidiaries | Senior debt
Debt Instrument [Line Items]
Borrowed funds	4,604	4,615
Basis adjustments - Fair value accounting hedges	(173)
Subsidiaries | Subordinated debt
Debt Instrument [Line Items]
Borrowed funds	3,091	$ 3,125
Basis adjustments - Fair value accounting hedges	$ (195)