Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Marketable Debt and Equity Securities
Fair Value	$ 2,111.1us-gaap_AvailableForSaleSecurities	$ 1,245.9us-gaap_AvailableForSaleSecurities
Gross Unrealized Gains	0.7	0.4
Gross Unrealized Losses	(2.4)	(0.3)
Amortized Cost	2,112.8	1,245.8
Corporate debt securities Current
Marketable Debt and Equity Securities
Fair Value	370.4	100.7
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(0.2)	0
Amortized Cost	370.6	100.7
Corporate debt securities Non-current
Marketable Debt and Equity Securities
Fair Value	692.6	339.1
Gross Unrealized Gains	0.2	0.4
Gross Unrealized Losses	(1.5)	(0.1)
Amortized Cost	693.9	338.8
Government securities Current
Marketable Debt and Equity Securities
Fair Value	269.9	519.5
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(0.1)	0
Amortized Cost	270.0	519.5
Government securities Non-current
Marketable Debt and Equity Securities
Fair Value	579.9	155.2
Gross Unrealized Gains	0.3	0
Gross Unrealized Losses	(0.4)	(0.1)
Amortized Cost	580.0	155.3
Mortgage and other asset backed securities Current
Marketable Debt and Equity Securities
Fair Value	0.2	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Amortized Cost	0.2	0
Mortgage and other asset backed securities Non-current
Marketable Debt and Equity Securities
Fair Value	198.1	131.4
Gross Unrealized Gains	0.2	0
Gross Unrealized Losses	(0.2)	(0.1)
Amortized Cost	198.1	131.5
Marketable equity securities
Marketable Debt and Equity Securities
Fair Value	6.9	11.2
Gross Unrealized Gains	1.2	8.7
Gross Unrealized Losses	(0.2)	0
Amortized Cost	$ 5.9	$ 2.5

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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