Loans (Loans - Delinquency Status) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 608.6	$ 417.3
Current	37,921.8	29,304.0
Total	38,530.4	30,998.9	$ 31,247.0
30-59 Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	383.4	205.0
60-89 Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	68.2	116.0
90 or more Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	157.0	96.3
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	345.4	353.5
Current	29,677.3	24,012.1
Total	30,022.7	24,393.4
Commercial Banking | Commercial Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	133.4	135.5
Current	17,059.9	13,777.3
Total	17,193.3	13,912.8
Commercial Banking | Real Estate Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	23.4	47.2
Current	7,693.5	5,307.5
Total	7,716.9	5,382.5
Commercial Banking | Business Capital
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	188.6	170.8
Current	4,863.2	4,867.7
Total	5,051.8	5,038.5
Commercial Banking | Rail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	60.7	59.6
Total	60.7	59.6
Commercial Banking | 30-59 Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	221.0	173.1
Commercial Banking | 30-59 Past Due | Commercial Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	70.7	58.7
Commercial Banking | 30-59 Past Due | Real Estate Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	21.0	0.6
Commercial Banking | 30-59 Past Due | Business Capital
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	129.3	113.8
Commercial Banking | 60-89 Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	37.4	109.4
Commercial Banking | 60-89 Past Due | Commercial Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1.8	27.8
Commercial Banking | 60-89 Past Due | Real Estate Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1.5	46.6
Commercial Banking | 60-89 Past Due | Business Capital
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	34.1	35.0
Commercial Banking | 90 or more Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	87.0	71.0
Commercial Banking | 90 or more Past Due | Commercial Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	60.9	49.0
Commercial Banking | 90 or more Past Due | Real Estate Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.9
Commercial Banking | 90 or more Past Due | Business Capital
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	25.2	22.0
Consumer Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	263.2	63.8
Current	8,244.5	5,291.9
Total	8,507.7	6,605.5
Consumer Banking | Legacy Consumer Mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	205.0	36.5
Current	1,887.4	795.2
Total	2,092.4	2,081.5
Consumer Banking | Consumer and Community Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	58.2
Current	6,357.1
Total	6,415.3
Consumer Banking | 30-59 Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	162.4	31.9
Consumer Banking | 30-59 Past Due | Legacy Consumer Mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	120.1	15.5
Consumer Banking | 30-59 Past Due | Consumer and Community Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	42.3
Consumer Banking | 60-89 Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	30.8	6.6
Consumer Banking | 60-89 Past Due | Legacy Consumer Mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	25.2	3.3
Consumer Banking | 60-89 Past Due | Consumer and Community Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5.6
Consumer Banking | 90 or more Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	70.0	25.3
Consumer Banking | 90 or more Past Due | Legacy Consumer Mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	59.7	17.7
Consumer Banking | 90 or more Past Due | Consumer and Community Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10.3
Consumer Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	$ 7,833.6	5,979.4
Consumer Loans | Consumer and Community Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		27.3
Current		4,496.7
Total		4,524.0
Consumer Loans | 30-59 Past Due | Consumer and Community Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		16.4
Consumer Loans | 60-89 Past Due | Consumer and Community Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		3.3
Consumer Loans | 90 or more Past Due | Consumer and Community Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		7.6
PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total		1,277.6
PCI Loans | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total		27.8
PCI Loans | Commercial Banking | Real Estate Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total		27.8
PCI Loans | Consumer Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total		1,249.8
PCI Loans | Consumer Banking | Legacy Consumer Mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total		$ 1,249.8