Loans (Impaired Loans) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 2,134.1	$ 2,571.6
Unpaid Principal Balance	3,065.7	3,685.0
Related Allowance	45.1	47.3
Average Recorded Investment	2,391.2	2,685.8
Commercial Finance \| Commercial Banking
Financing Receivable, Impaired [Line Items]
With no related allowance, Recorded Investment	51.9	54.3
With related allowance, Recorded Investment	95.9	143.0
With no related allowance, Unpaid Principal Balance	72.7	72.2
With related allowance, Unpaid Principal Balance	96.1	146.2
Related Allowance	21.3	25.5
With no related allowance, Average Recorded Investment	59.9	29.5
With related allowance, Average Recorded Investment	136.6	132.1
Business Capital \| Commercial Banking
Financing Receivable, Impaired [Line Items]
With no related allowance, Recorded Investment	11.7	0.5
With related allowance, Recorded Investment	10.5	6.6
With no related allowance, Unpaid Principal Balance	13.4	1.8
With related allowance, Unpaid Principal Balance	10.5	6.6
Related Allowance	4.3	4.2
With no related allowance, Average Recorded Investment	5.7	5.1
With related allowance, Average Recorded Investment	14.2	8.2
Real Estate Finance \| Commercial Banking
Financing Receivable, Impaired [Line Items]
With no related allowance, Recorded Investment	0.0	0.7
With related allowance, Recorded Investment	2.7	16.7
With no related allowance, Unpaid Principal Balance	0.0	0.7
With related allowance, Unpaid Principal Balance	2.8	16.8
Related Allowance	0.4	4.0
With no related allowance, Average Recorded Investment	0.4	1.3
With related allowance, Average Recorded Investment	5.6	5.2
Impaired Loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	172.7	221.8
Unpaid Principal Balance	195.5	244.3
Related Allowance	26.0	33.7
Average Recorded Investment	222.4	181.4
Interest income recorded	2.4	1.6
Interest income recognized using cash basis method	0.0	0.6
PCI Loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,961.4	2,349.8
Unpaid Principal Balance	2,870.2	3,440.7
Related Allowance	19.1	13.6
Average Recorded Investment	2,168.8	2,504.4
PCI Loans \| Commercial Finance \| Commercial Banking
Financing Receivable, Impaired [Line Items]
Recorded Investment	10.6	42.7
Unpaid Principal Balance	16.4	70.0
Related Allowance	0.7	2.4
PCI Loans \| Real Estate Finance \| Commercial Banking
Financing Receivable, Impaired [Line Items]
Recorded Investment	45.1	70.5
Unpaid Principal Balance	60.1	108.1
Related Allowance	$ 7.0	$ 4.9

Impaired financing receivable, interest income.

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Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

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Amount of interest income recognized on a cash-basis method of accounting that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

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-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

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