Consolidated Statements of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest and dividend income:
Commercial real estate	$ 556.4	$ 463.4	$ 405.7
Commercial and industrial	443.6	365.7	298.8
Equipment financing	253.8	212.3	152.1
Residential mortgage	329.1	236.2	207.5
Home equity and other consumer	106.1	88.6	80.0
Interest and Fee Income, Loans and Leases Held-in-portfolio, Total	1,689.0	1,366.2	1,144.1
Securities	186.5	184.2	153.7
Short-term investments	4.8	5.0	3.7
Loans held-for-sale	0.8	0.9	0.9
Total interest and dividend income	1,881.1	1,556.3	1,302.4
Interest expense:
Deposits (note 10)	356.9	216.1	130.7
Borrowings (note 11)	77.0	70.9	41.3
Notes and debentures	34.9	33.3	29.9
Total interest expense	468.8	320.3	201.9
Net interest income	1,412.3	1,236.0	1,100.5
Provision for loan losses (note 5)	28.3	30.0	26.0
Net interest income after provision for loan losses	1,384.0	1,206.0	1,074.5
Non-interest income:
Operating lease income (note 6)	51.2
Operating lease income (note 6)		44.9	43.8
Cash management fees	28.4	27.1	26.1
Net security gains (losses) (note 4)	0.2	(9.8)	(25.4)
Other non-interest income (notes 4 and 6)	85.9	50.9	62.6
Total non-interest income	431.1	366.4	352.9
Non-interest expense:
Compensation and benefits (notes 18 and 19)	646.2	562.9	522.7
Occupancy and equipment (note 8)	185.9	168.2	159.6
Professional and outside services	98.2	77.6	81.5
Regulatory assessments	26.1	37.9	41.7
Operating lease expense	38.8	36.4	35.2
Amortization of other acquisition-related intangible assets (note 7)	32.5	21.8	30.0
Other non-interest expense	135.0	91.3	89.6
Total non-interest expense	1,162.7	996.1	960.3
Income before income tax expense	652.4	576.3	467.1
Income tax expense (benefit)	132.0	108.2	129.9
Net income	520.4	468.1	337.2
Preferred stock dividend	14.1	14.1	14.1
Net income available to common shareholders	$ 506.3	$ 454.0	$ 323.1
Earnings per common share (note 16):
Basic (in dollars per share)	$ 1.28	$ 1.30	$ 0.98
Diluted (in dollars per share)	$ 1.27	$ 1.29	$ 0.97
Bank Service Charges [Member]
Non-interest income:
Revenue from contract with customer	$ 107.5	$ 99.9	$ 98.5
Investment Management Fees [Member]
Non-interest income:
Revenue from contract with customer	67.6	68.7	66.5
Commercial Banking Lending Fees [Member]
Non-interest income:
Revenue from contract with customer	42.7	37.3	35.5
Insurance Revenue [Member]
Non-interest income:
Revenue from contract with customer	37.0	34.6	33.2
Brokerage Commissions [Member]
Non-interest income:
Revenue from contract with customer	$ 10.6	$ 12.8	$ 12.1