Loans (Commercial Loans - By Risk Rating) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 38,530.4	$ 30,998.9	$ 31,247.0
PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans		1,277.6
Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
Loans	30,022.7	24,393.4
Consumer Banking
Financing Receivable, Recorded Investment [Line Items]
Loans	8,507.7	6,605.5
Commercial Loans
Financing Receivable, Recorded Investment [Line Items]
2020	4,010.8
2019	8,007.3
2018	6,360.8
2017	3,161.5
2016	1,820.1
2015 & Prior	3,031.2
Revolving Loans Amortized Cost Basis	4,198.9
Revolving Loans Converted to Term Loans Amortized Cost Basis	106.2
Loans	30,696.8	25,019.5
Commercial Loans | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans		27.8
Commercial Loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		22,784.8
Commercial Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		1,027.2
Commercial Loans | Classified- accrual
Financing Receivable, Recorded Investment [Line Items]
Loans		871.5
Commercial Loans | Classified- non-accrual
Financing Receivable, Recorded Investment [Line Items]
Loans		308.2
Commercial Loans | Real Estate Finance | Pass | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans		20.7
Commercial Loans | Commercial Banking
Financing Receivable, Recorded Investment [Line Items]
2020	3,960.4
2019	7,802.6
2018	6,232.7
2017	3,061.3
2016	1,751.2
2015 & Prior	2,919.7
Revolving Loans Amortized Cost Basis	4,188.6
Revolving Loans Converted to Term Loans Amortized Cost Basis	106.2
Loans	30,022.7	24,393.4
Commercial Loans | Commercial Banking | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans		27.8
Commercial Loans | Commercial Banking | Pass
Financing Receivable, Recorded Investment [Line Items]
2020	3,852.5
2019	7,403.5
2018	5,807.9
2017	2,534.6
2016	1,541.6
2015 & Prior	2,386.8
Revolving Loans Amortized Cost Basis	3,647.1
Revolving Loans Converted to Term Loans Amortized Cost Basis	98.8
Loans	27,272.8	22,195.2
Commercial Loans | Commercial Banking | Special Mention
Financing Receivable, Recorded Investment [Line Items]
2020	71.1
2019	275.9
2018	229.0
2017	260.3
2016	78.0
2015 & Prior	192.6
Revolving Loans Amortized Cost Basis	257.2
Revolving Loans Converted to Term Loans Amortized Cost Basis	5.8
Loans	1,369.9	1,024.8
Commercial Loans | Commercial Banking | Classified- accrual
Financing Receivable, Recorded Investment [Line Items]
2020	36.7
2019	109.3
2018	119.6
2017	227.5
2016	93.1
2015 & Prior	253.5
Revolving Loans Amortized Cost Basis	241.7
Revolving Loans Converted to Term Loans Amortized Cost Basis	1.6
Loans	1,083.0	837.6
Commercial Loans | Commercial Banking | Classified- non-accrual
Financing Receivable, Recorded Investment [Line Items]
2020	0.1
2019	13.9
2018	76.2
2017	38.9
2016	38.5
2015 & Prior	86.8
Revolving Loans Amortized Cost Basis	42.6
Loans	297.0	308.0
Commercial Loans | Commercial Banking | Commercial Finance
Financing Receivable, Recorded Investment [Line Items]
2020	2,796.0
2019	3,343.1
2018	3,075.6
2017	1,302.6
2016	646.1
2015 & Prior	1,810.3
Revolving Loans Amortized Cost Basis	4,114.0
Revolving Loans Converted to Term Loans Amortized Cost Basis	105.6
Loans	17,193.3	13,912.8
Commercial Loans | Commercial Banking | Commercial Finance | Pass
Financing Receivable, Recorded Investment [Line Items]
2020	2,714.0
2019	3,256.1
2018	2,903.2
2017	1,080.7
2016	518.6
2015 & Prior	1,350.1
Revolving Loans Amortized Cost Basis	3,572.5
Revolving Loans Converted to Term Loans Amortized Cost Basis	98.2
Loans	15,493.4	12,601.1
Commercial Loans | Commercial Banking | Commercial Finance | Special Mention
Financing Receivable, Recorded Investment [Line Items]
2020	54.2
2019	68.1
2018	86.7
2017	54.0
2016	27.7
2015 & Prior	139.6
Revolving Loans Amortized Cost Basis	257.2
Revolving Loans Converted to Term Loans Amortized Cost Basis	5.8
Loans	693.3	450.7
Commercial Loans | Commercial Banking | Commercial Finance | Classified- accrual
Financing Receivable, Recorded Investment [Line Items]
2020	27.8
2019	18.9
2018	27.2
2017	152.3
2016	69.0
2015 & Prior	238.3
Revolving Loans Amortized Cost Basis	241.7
Revolving Loans Converted to Term Loans Amortized Cost Basis	1.6
Loans	776.8	614.3
Commercial Loans | Commercial Banking | Commercial Finance | Classified- non-accrual
Financing Receivable, Recorded Investment [Line Items]
2018	58.5
2017	15.6
2016	30.8
2015 & Prior	82.3
Revolving Loans Amortized Cost Basis	42.6
Loans	229.8	246.7
Commercial Loans | Commercial Banking | Real Estate Finance
Financing Receivable, Recorded Investment [Line Items]
2020	574.1
2019	2,413.0
2018	1,781.0
2017	1,103.8
2016	819.7
2015 & Prior	968.7
Revolving Loans Amortized Cost Basis	56.6
Loans	7,716.9	5,382.5
Commercial Loans | Commercial Banking | Real Estate Finance | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans		27.8
Commercial Loans | Commercial Banking | Real Estate Finance | Pass
Financing Receivable, Recorded Investment [Line Items]
2020	574.1
2019	2,300.8
2018	1,712.7
2017	907.6
2016	789.7
2015 & Prior	909.7
Revolving Loans Amortized Cost Basis	56.6
Loans	7,251.2	5,007.0
Commercial Loans | Commercial Banking | Real Estate Finance | Special Mention
Financing Receivable, Recorded Investment [Line Items]
2019	109.0
2018	59.0
2017	167.6
2016	26.4
2015 & Prior	49.0
Loans	411.0	341.0
Commercial Loans | Commercial Banking | Real Estate Finance | Classified- accrual
Financing Receivable, Recorded Investment [Line Items]
2019	3.2
2018	9.0
2017	28.6
2016	3.6
2015 & Prior	8.8
Loans	53.2	6.3
Commercial Loans | Commercial Banking | Real Estate Finance | Classified- non-accrual
Financing Receivable, Recorded Investment [Line Items]
2018	0.3
2015 & Prior	1.2
Loans	1.5	0.4
Commercial Loans | Commercial Banking | Rail
Financing Receivable, Recorded Investment [Line Items]
2019	0.9
2016	3.2
2015 & Prior	56.6
Loans	60.7	59.6
Commercial Loans | Commercial Banking | Rail | Pass
Financing Receivable, Recorded Investment [Line Items]
2019	0.9
2016	3.2
2015 & Prior	56.6
Loans	60.7	59.6
Commercial Loans | Commercial Banking | Business Capital
Financing Receivable, Recorded Investment [Line Items]
2020	590.3
2019	2,045.6
2018	1,376.1
2017	654.9
2016	282.2
2015 & Prior	84.1
Revolving Loans Amortized Cost Basis	18.0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0.6
Loans	5,051.8	5,038.5
Commercial Loans | Commercial Banking | Business Capital | Pass
Financing Receivable, Recorded Investment [Line Items]
2020	564.4
2019	1,845.7
2018	1,192.0
2017	546.3
2016	230.1
2015 & Prior	70.4
Revolving Loans Amortized Cost Basis	18.0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0.6
Loans	4,467.5	4,527.5
Commercial Loans | Commercial Banking | Business Capital | Special Mention
Financing Receivable, Recorded Investment [Line Items]
2020	16.9
2019	98.8
2018	83.3
2017	38.7
2016	23.9
2015 & Prior	4.0
Loans	265.6	233.1
Commercial Loans | Commercial Banking | Business Capital | Classified- accrual
Financing Receivable, Recorded Investment [Line Items]
2020	8.9
2019	87.2
2018	83.4
2017	46.6
2016	20.5
2015 & Prior	6.4
Loans	253.0	217.0
Commercial Loans | Commercial Banking | Business Capital | Classified- non-accrual
Financing Receivable, Recorded Investment [Line Items]
2020	0.1
2019	13.9
2018	17.4
2017	23.3
2016	7.7
2015 & Prior	3.3
Loans	65.7	60.9
Commercial Loans | Consumer Banking
Financing Receivable, Recorded Investment [Line Items]
Loans		626.1
Commercial Loans | Consumer Banking | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans		589.6
Commercial Loans | Consumer Banking | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans		2.4
Commercial Loans | Consumer Banking | Classified- accrual
Financing Receivable, Recorded Investment [Line Items]
Loans		33.9
Commercial Loans | Consumer Banking | Classified- non-accrual
Financing Receivable, Recorded Investment [Line Items]
Loans		0.2
Commercial Loans | Consumer Banking | Consumer and Community Banking - SBA Loans
Financing Receivable, Recorded Investment [Line Items]
2020	50.4
2019	204.7
2018	128.1
2017	100.2
2016	68.9
2015 & Prior	111.5
Revolving Loans Amortized Cost Basis	10.3
Loans	674.1	626.1
Commercial Loans | Consumer Banking | Consumer and Community Banking - SBA Loans | Pass
Financing Receivable, Recorded Investment [Line Items]
2020	50.4
2019	202.3
2018	118.5
2017	90.7
2016	62.9
2015 & Prior	90.8
Revolving Loans Amortized Cost Basis	10.0
Loans	625.6	589.6
Commercial Loans | Consumer Banking | Consumer and Community Banking - SBA Loans | Special Mention
Financing Receivable, Recorded Investment [Line Items]
2019	1.0
2018	2.0
2017	0.5
2015 & Prior	3.0
Loans	6.5	2.4
Commercial Loans | Consumer Banking | Consumer and Community Banking - SBA Loans | Classified- accrual
Financing Receivable, Recorded Investment [Line Items]
2019	1.4
2018	7.6
2017	8.8
2016	6.0
2015 & Prior	17.2
Revolving Loans Amortized Cost Basis	0.3
Loans	41.3	33.9
Commercial Loans | Consumer Banking | Consumer and Community Banking - SBA Loans | Classified- non-accrual
Financing Receivable, Recorded Investment [Line Items]
2017	0.2
2015 & Prior	0.5
Loans	$ 0.7	$ 0.2