Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014 item	Dec. 31, 2013 item
Derivative
Number of Hedging instruments	0	0
Derivatives not designated as hedging instruments
Derivative
Notional Amount	4,344.7	3,499.9
Derivative Assets	53.2	47.9
Derivative Liabilities	52.9	46.3
Derivatives not designated as hedging instruments \| Option contracts
Derivative
Notional Amount	1.9	1.9
Derivative Assets	0.4	0.4
Derivatives not designated as hedging instruments \| Interest-Rate Contracts
Derivative
Notional Amount	3,531.8	3,024.0
Derivative Assets	45.5	43.8
Derivative Liabilities	46.0	42.8
Derivatives not designated as hedging instruments \| Interest-Rate Contracts \| Options purchased \| Purchase
Derivative
Notional Amount		1.5
Derivative Assets		0.6
Derivative Liabilities		0.6
Derivatives not designated as hedging instruments \| Interest-Rate Contracts \| Options purchased \| Sale
Derivative
Notional Amount		1.5
Derivatives not designated as hedging instruments \| Interest-Rate Swaps
Derivative
Notional Amount	3,094.5	2,769.4
Derivative Assets	44.7	42.7
Derivative Liabilities	45.2	41.7
Derivatives not designated as hedging instruments \| Interest Rate Caps, Floors and Collars
Derivative
Notional Amount	437.3	251.6
Derivative Assets	0.8	0.5
Derivative Liabilities	0.8	0.5
Derivatives not designated as hedging instruments \| Spot and forward contracts
Derivative
Notional Amount	802.7	461.4
Derivative Assets	6.1	3.5
Derivative Liabilities	6.6	3.3
Derivatives not designated as hedging instruments \| Foreign Exchange Contracts
Derivative
Notional Amount	808.7	474.0
Derivative Assets	6.4	3.7
Derivative Liabilities	6.9	3.5
Derivatives not designated as hedging instruments \| Foreign Exchange Contracts \| Options purchased \| Purchase
Derivative
Notional Amount	3.0	6.3
Derivative Assets	0.1
Derivative Liabilities	0.1
Derivatives not designated as hedging instruments \| Foreign Exchange Contracts \| Options purchased \| Sale
Derivative
Notional Amount	3.0	6.3
Derivative Assets	0.2	0.2
Derivative Liabilities	0.2	0.2
Equity Warrants \| Derivatives not designated as hedging instruments
Derivative
Notional Amount	2.3
Derivative Assets	0.9

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

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- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and elected not to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=34720828&loc=SL20225862-175312

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- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and elected not to be offset.

+ References

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- Definition

The number of derivative instruments of a particular group held by the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1A

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5579245-113959

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