Borrowed Funds (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Borrowed funds	$ 42,110	$ 60,263
Parent Company [Member]
Debt Instrument [Line Items]
Borrowed funds	10,690	9,825
Parent Company [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Borrowed funds	9,674	8,843
Basis adjustments - Fair value accounting hedges	763
Parent Company [Member] | Subordinated Debt [Member]
Debt Instrument [Line Items]
Borrowed funds	811	777
Basis adjustments - Fair value accounting hedges	63
Subsidiaries [Member]
Debt Instrument [Line Items]
Borrowed funds	28,114	41,660
Subsidiaries [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Borrowed funds	17,165	20,167
Basis adjustments - Fair value accounting hedges	555
Subsidiaries [Member] | Subordinated Debt [Member]
Debt Instrument [Line Items]
Borrowed funds	5,449	$ 5,152
Basis adjustments - Fair value accounting hedges	$ 469