Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair value of assets and liabilities measured on recurring basis
Short-term Investments	$ 381.2us-gaap_ShortTermInvestments	$ 360.7us-gaap_ShortTermInvestments
Fair value measurements recurring basis \| Level 1
Fair value of assets and liabilities measured on recurring basis
Short-term Investments	381.2	360.7
Total	381.2	360.7
Fair value measurements recurring basis \| Level 2
Fair value of assets and liabilities measured on recurring basis
Forward contracts	50.9	11.0
Total	50.9	11.0
Fair value measurements recurring basis \| Total
Fair value of assets and liabilities measured on recurring basis
Short-term Investments	381.2	360.7
Forward contracts	50.9	11.0
Total	$ 432.1	$ 371.7

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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- Definition

Fair value portion of liability contracts related to the exchange of different currencies, including, but not limited to, foreign currency options, forward (delivery or nondelivery) contracts, and swaps entered into.

+ References

No definition available.

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- Definition

Investments which are intended to be sold in the short term (usually less than one year or the normal operating cycle, whichever is longer) including trading securities, available-for-sale securities, held-to-maturity securities, and other short-term investments not otherwise listed in the existing taxonomy.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph g

-Article 7

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