Loans and Leases - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest	$ 169.0	$ 169.0	$ 180.0
Net loans and leases	55,872.0	55,872.0	57,269.0
Loans and leases	56,687.0	56,687.0	58,232.0
Troubled debt restructurings loans	274.0	274.0	307.0
C&I
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collateral for secured borrowings	177.0	177.0	167.0
Allowance for credit loss, writeoff, collateral	2.0	16.0
Loans Held For Sale, Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings loans	38.0	38.0	42.0
Commercial \| Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	32,528.0	32,528.0	33,104.0
Commercial \| Commercial and industrial \| Finance And Insurance Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	3,200.0	3,200.0
Commercial \| Commercial and industrial \| Loans to mortgage companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 4,876.0	$ 4,876.0	5,404.0
Percentage contributed	25.00%	25.00%
Commercial \| Commercial and industrial \| C&I
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 27,652.0	$ 27,652.0	27,700.0
Collateral for secured borrowings	151.0	151.0
Commercial \| Loans to mortgage companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	4,876.0	4,876.0	5,404.0
Commercial \| Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	12,292.0	12,292.0	12,275.0
Commercial \| Commercial real estate \| CRE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	12,292.0	12,292.0	12,275.0
Collateral for secured borrowings	26.0	26.0
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	10,865.0	10,865.0	11,725.0
Consumer \| Consumer Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	10,865.0	10,865.0	11,725.0
Consumer \| Consumer Real Estate \| HELOC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	2,151.0	2,151.0	2,420.0
Collateral for secured borrowings	8.0	8.0	9.0
Consumer \| Consumer Real Estate \| Real estate installment loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	8,714.0	8,714.0	9,305.0
Collateral for secured borrowings	23.0	23.0	26.0
Asset Pledged as Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net loans and leases	$ 37,200.0	$ 37,200.0	$ 38,600.0

Financing Receivable, Allowance for Credit Loss, Writeoff, Collateral

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