Outstanding Loans and Leases and Allowance for Credit Losses - Consumer Real Estate - Modification Programs (Details) - Consumer real estate - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total modifications	$ 444	$ 98	$ 815	$ 289
Modifications under government programs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total modifications	0	0	4	8
Modifications under proprietary programs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total modifications	417	50	740	136
Loans discharged in Chapter 7 bankruptcy
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total modifications	9	15	29	44
Trial modifications
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total modifications	$ 18	$ 33	$ 42	$ 101