Loans (Finance And Held For Sale Loans - Delinquency Status) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 395.9	$ 339.5
Current	27,852.3	27,482.4
Total	30,209.6	30,171.7
30 — 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	227.4	204.0
60 — 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	50.6	55.1
90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	117.9	80.4
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	297.4	250.2
Current	22,973.0	22,556.5
Total	23,326.1	22,919.9
Commercial Banking | 30 — 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	189.3	171.0
Commercial Banking | 60 — 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	34.8	43.0
Commercial Banking | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	73.3	36.2
Commercial Banking | Commercial Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	53.8	39.0
Current	9,987.9	10,193.8
Total	10,052.3	10,275.5
Commercial Banking | Commercial Finance | 30 — 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	4.5	21.4
Commercial Banking | Commercial Finance | 60 — 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0.0	0.0
Commercial Banking | Commercial Finance | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	49.3	17.6
Commercial Banking | Real Estate Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	12.8	0.1
Current	5,532.3	5,496.0
Total	5,590.2	5,566.6
Commercial Banking | Real Estate Finance | 30 — 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	8.7	0.1
Commercial Banking | Real Estate Finance | 60 — 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0.0	0.0
Commercial Banking | Real Estate Finance | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	4.1	0.0
Commercial Banking | Business Capital
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	224.7	202.3
Current	7,355.1	6,771.8
Total	7,579.8	6,974.1
Commercial Banking | Business Capital | 30 — 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	172.2	143.6
Commercial Banking | Business Capital | 60 — 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	33.4	42.4
Commercial Banking | Business Capital | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	19.1	16.3
Commercial Banking | Rail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	6.1	8.8
Current	97.7	94.9
Total	103.8	103.7
Commercial Banking | Rail | 30 — 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3.9	5.9
Commercial Banking | Rail | 60 — 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1.4	0.6
Commercial Banking | Rail | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0.8	2.3
Consumer Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	79.6	78.2
Current	4,834.9	4,727.0
Total	6,820.2	7,041.8
Consumer Banking | 30 — 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	36.3	30.0
Consumer Banking | 60 — 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	8.1	11.0
Consumer Banking | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	35.2	37.2
Consumer Banking | LCM
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	69.1	65.3
Current	1,358.5	2,563.6
Total	3,331.1	4,862.7
Consumer Banking | LCM | 30 — 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	26.7	22.6
Consumer Banking | LCM | 60 — 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	7.6	6.1
Consumer Banking | LCM | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	34.8	36.6
Consumer Banking | Other Consumer Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	10.5	12.9
Current	3,476.4	2,163.4
Total	3,489.1	2,179.1
Consumer Banking | Other Consumer Banking | 30 — 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	9.6	7.4
Consumer Banking | Other Consumer Banking | 60 — 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0.5	4.9
Consumer Banking | Other Consumer Banking | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0.4	0.6
PCI Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	1,961.4	2,349.8
PCI Loans | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	55.7	113.2
PCI Loans | Commercial Banking | Commercial Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	10.6	42.7
PCI Loans | Commercial Banking | Real Estate Finance
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	45.1	70.5
PCI Loans | Commercial Banking | Business Capital
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0.0	0.0
PCI Loans | Commercial Banking | Rail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	0.0	0.0
PCI Loans | Consumer Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	1,905.7	2,236.6
PCI Loans | Consumer Banking | LCM
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	1,903.5	2,233.8
PCI Loans | Consumer Banking | Other Consumer Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	2.2	2.8
Non-Strategic Portfolios | Non-Strategic Portfolios
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	18.9	11.1
Current	44.4	198.9
Total	63.3	210.0
Non-Strategic Portfolios | Non-Strategic Portfolios | 30 — 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1.8	3.0
Non-Strategic Portfolios | Non-Strategic Portfolios | 60 — 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	7.7	1.1
Non-Strategic Portfolios | Non-Strategic Portfolios | 90 Days or Greater
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	9.4	7.0
Non-Strategic Portfolios | PCI Loans | Non-Strategic Portfolios
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total	$ 0.0	$ 0.0