Borrowed Funds (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Borrowed funds	$ 47,026	$ 60,263
Parent Company [Member]
Debt Instrument [Line Items]
Borrowed funds	11,506	9,825
Parent Company [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Borrowed funds	10,486	8,843
Basis adjustments - Fair value accounting hedges	820
Parent Company [Member] | Subordinated Debt [Member]
Debt Instrument [Line Items]
Borrowed funds	815	777
Basis adjustments - Fair value accounting hedges	67
Subsidiaries [Member]
Debt Instrument [Line Items]
Borrowed funds	31,198	41,660
Subsidiaries [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Borrowed funds	17,219	20,167
Basis adjustments - Fair value accounting hedges	608
Subsidiaries [Member] | Subordinated Debt [Member]
Debt Instrument [Line Items]
Borrowed funds	5,479	$ 5,152
Basis adjustments - Fair value accounting hedges	$ 496