Loans and Leases - Narrative (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest	$ 143,000,000	$ 143,000,000	$ 180,000,000
Net loans and leases	54,701,000,000	54,701,000,000	57,269,000,000
Loans and leases	55,435,000,000	55,435,000,000	58,232,000,000
Troubled debt restructurings loans	239,000,000	239,000,000	307,000,000
C&I
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collateral for secured borrowings	174,000,000	174,000,000	167,000,000
Allowance for credit loss, writeoff, collateral	9,000,000	25,000,000
Loans Held For Sale, Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings loans	37,000,000	37,000,000	42,000,000
Commercial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	31,516,000,000	31,516,000,000	33,104,000,000
Commercial | Commercial and industrial | Finance And Insurance Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	3,200,000,000	3,200,000,000
Commercial | Commercial and industrial | Loans to mortgage companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 5,139,000,000	$ 5,139,000,000	5,404,000,000
Percentage contributed	26.00%	26.00%
Commercial | Commercial and industrial | C&I
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 26,377,000,000	$ 26,377,000,000	27,700,000,000
Collateral for secured borrowings	161,000,000	161,000,000
Commercial | Loans to mortgage companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	5,139,000,000	5,139,000,000	5,404,000,000
Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	12,194,000,000	12,194,000,000	12,275,000,000
Commercial | Commercial real estate | CRE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	12,194,000,000	12,194,000,000	12,275,000,000
Collateral for secured borrowings	13,000,000	13,000,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	10,787,000,000	10,787,000,000	11,725,000,000
Consumer | Consumer Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	10,787,000,000	10,787,000,000	11,725,000,000
Allowance for credit loss, writeoff, collateral	0	0
Consumer | Consumer Real Estate | HELOC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	2,041,000,000	2,041,000,000	2,420,000,000
Collateral for secured borrowings	8,000,000	8,000,000	9,000,000
Consumer | Consumer Real Estate | Real estate installment loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	8,746,000,000	8,746,000,000	9,305,000,000
Collateral for secured borrowings	21,000,000	21,000,000	26,000,000
Asset Pledged as Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net loans and leases	$ 37,400,000,000	$ 37,400,000,000	$ 38,600,000,000