Loans - Summary of Loans by Loan Portfolio Segment and Class (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 44,284.0	$ 43,596.1
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	31,710.0	30,714.3
Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	14,651.6	14,762.3
Commercial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	9,097.7	8,693.2
Commercial | Equipment financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,012.7	4,910.4
Commercial | MWABL
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,948.0	2,348.4
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	12,574.0	12,881.8
Retail | Adjustable-rate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,825.2	7,064.8
Retail | Fixed-rate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,256.7	3,253.3
Retail | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	10,081.9	10,318.1
Retail | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,349.9	2,406.5
Retail | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	142.2	157.2
Retail | Home equity and other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 2,492.1	$ 2,563.7