Debt (Convertible Debenture Terms) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014
Debt Disclosure [Abstract]
Outstanding principal amount	$ 1,500.0us-gaap_DebtInstrumentFaceAmount
Unamortized debt discount	525.6
Net debt carrying amount	974.4us-gaap_ConvertibleDebtNoncurrent
Equity Component carrying amount	$ 543.6
Conversion rate (shares of common stock per $1,000 of principal amount)	13.3645
Effective conversion price (per $1,000 of principal amount) per share	$ 74.8244

Carrying amount of long-term convertible debt as of the balance sheet date, net of the amount due in the next twelve months or greater than the normal operating cycle, if longer. The debt is convertible into another form of financial instrument, typically the entity's common stock.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

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

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- Definition

The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (a)

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- Definition

The price per share of the conversion feature embedded in the debt instrument.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 20

-Section 50

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- Definition

Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

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-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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-Glossary Conversion Rate

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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-Publisher FASB

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- Definition

The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

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