Borrowed Funds (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Borrowed funds	$ 73,399	$ 60,263
Parent Company [Member]
Debt Instrument [Line Items]
Borrowed funds	11,461	9,825
Parent Company [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Borrowed funds	10,442	8,843
Basis adjustments - Fair value accounting hedges	778
Parent Company [Member] | Subordinated Debt [Member]
Debt Instrument [Line Items]
Borrowed funds	814	777
Basis adjustments - Fair value accounting hedges	65
Subsidiaries [Member]
Debt Instrument [Line Items]
Borrowed funds	49,943	41,660
Subsidiaries [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Borrowed funds	20,996	20,167
Basis adjustments - Fair value accounting hedges	592
Subsidiaries [Member] | Subordinated Debt [Member]
Debt Instrument [Line Items]
Borrowed funds	5,456	$ 5,152
Basis adjustments - Fair value accounting hedges	$ 473