Loans (Finance and Held For Sale Receivables - Delinquency Status) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 330.9	$ 339.5
Current	27,184.6	27,482.4
Total	29,561.9	30,171.7
30–59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	160.4	204.0
60–89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	47.2	55.1
90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	123.3	80.4
PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	2,046.4	2,349.8
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	23,283.3	23,538.3
Commercial Banking | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	68.1	116.0
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	256.7	250.2
Current	22,473.0	22,556.5
Total	22,795.5	22,919.9
Commercial Banking | 30–59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	126.9	171.0
Commercial Banking | 60–89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	42.1	43.0
Commercial Banking | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	87.7	36.2
Commercial Banking | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	65.8	113.2
Commercial Banking | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	22,795.5	22,919.9
Commercial Banking | Commercial Banking | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	65.8	113.2
Commercial Banking | Commercial Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	71.9	39.0
Current	9,312.1	10,193.8
Total	9,396.4	10,275.5
Commercial Banking | Commercial Finance | 30–59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	21.4
Commercial Banking | Commercial Finance | 60–89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	9.4	0.0
Commercial Banking | Commercial Finance | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	62.5	17.6
Commercial Banking | Commercial Finance | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	12.4	42.7
Commercial Banking | Commercial Finance | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	9,396.4	10,275.5
Commercial Banking | Commercial Finance | Commercial Banking | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	12.4	42.7
Commercial Banking | Real Estate Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2.8	0.1
Current	5,507.8	5,496.0
Total	5,564.0	5,566.6
Commercial Banking | Real Estate Finance | 30–59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.2	0.1
Commercial Banking | Real Estate Finance | 60–89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	0.0
Commercial Banking | Real Estate Finance | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2.6	0.0
Commercial Banking | Real Estate Finance | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	53.4	70.5
Commercial Banking | Real Estate Finance | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	5,564.0	5,566.6
Commercial Banking | Real Estate Finance | Commercial Banking | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	53.4	70.5
Commercial Banking | Business Capital
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	180.0	202.3
Current	7,550.6	6,771.8
Total	7,730.6	6,974.1
Commercial Banking | Business Capital | 30–59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	126.0	143.6
Commercial Banking | Business Capital | 60–89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	32.4	42.4
Commercial Banking | Business Capital | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	21.6	16.3
Commercial Banking | Business Capital | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0.0	0.0
Commercial Banking | Business Capital | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	7,730.6	6,974.1
Commercial Banking | Business Capital | Commercial Banking | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0.0	0.0
Commercial Banking | Rail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2.0	8.8
Current	102.5	94.9
Total	104.5	103.7
Commercial Banking | Rail | 30–59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.7	5.9
Commercial Banking | Rail | 60–89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.3	0.6
Commercial Banking | Rail | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1.0	2.3
Commercial Banking | Rail | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0.0	0.0
Commercial Banking | Rail | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	104.5	103.7
Commercial Banking | Rail | Commercial Banking | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0.0	0.0
Consumer Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	70.5	78.2
Current	4,627.5	4,727.0
Total	6,678.6	7,041.8
Consumer Banking | 30–59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	33.5	30.0
Consumer Banking | 60–89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5.1	11.0
Consumer Banking | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	31.9	37.2
Consumer Banking | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	1,980.6	2,236.6
Consumer Banking | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	400.0	408.4
Consumer Banking | Commercial Banking | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	2.3	2.8
Consumer Banking | Legacy Consumer Mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	66.8	65.3
Current	2,320.1	2,563.6
Total	4,365.2	4,862.7
Consumer Banking | Legacy Consumer Mortgages | 30–59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	30.2	22.6
Consumer Banking | Legacy Consumer Mortgages | 60–89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5.1	6.1
Consumer Banking | Legacy Consumer Mortgages | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	31.5	36.6
Consumer Banking | Legacy Consumer Mortgages | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	1,978.3	2,233.8
Consumer Banking | Other Consumer Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3.7	12.9
Current	2,307.4	2,163.4
Total	2,313.4	2,179.1
Consumer Banking | Other Consumer Banking | 30–59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3.3	7.4
Consumer Banking | Other Consumer Banking | 60–89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	4.9
Consumer Banking | Other Consumer Banking | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.4	0.6
Consumer Banking | Other Consumer Banking | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	2.3	2.8
Consumer Banking | Other Consumer Banking | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	400.0	408.4
Consumer Banking | Other Consumer Banking | Commercial Banking | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	2.3	2.8
Non-Strategic Portfolios | Non- Strategic Portfolios
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3.7	11.1
Current	84.1	198.9
Total	87.8	210.0
Non-Strategic Portfolios | Non- Strategic Portfolios | 30–59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	3.0
Non-Strategic Portfolios | Non- Strategic Portfolios | 60–89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.0	1.1
Non-Strategic Portfolios | Non- Strategic Portfolios | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3.7	7.0
Non-Strategic Portfolios | PCI Loans | Non- Strategic Portfolios
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0.0	0.0
Non-Strategic Portfolios | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	87.8	210.0
Non-Strategic Portfolios | Commercial Banking | PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	$ 0.0	$ 0.0