Outstanding Loans and Leases and Allowance for Credit Losses - Consumer Real Estate - Modification Programs (Details) - Consumer real estate - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total modifications	$ 715	$ 478	$ 999
Modifications under government programs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total modifications	13	35	61
Modifications under proprietary programs
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total modifications	570	174	523
Loans discharged in Chapter 7 bankruptcy
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total modifications	53	68	130
Trial modifications
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total modifications	$ 79	$ 201	$ 285