Financial Instruments (Details 1) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Marketable Debt and Equity Securities
Fair Value	$ 3,008.2	$ 5,172.5
Gross Unrealized Gains	0.5	2.3
Gross Unrealized Losses	(3.3)	(2.8)
Amortized Cost	3,011.0	5,173.0
Corporate debt securities Current
Marketable Debt and Equity Securities
Fair Value	912.9	1,039.3
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(0.8)	(0.2)
Amortized Cost	913.7	1,039.5
Corporate debt securities Non-current
Marketable Debt and Equity Securities
Fair Value	645.0	1,570.5
Gross Unrealized Gains	0.3	0.9
Gross Unrealized Losses	(0.7)	0.0
Amortized Cost	645.4	1,569.6
Government securities Current
Marketable Debt and Equity Securities
Fair Value	895.0	1,075.1
Gross Unrealized Gains	0.0	0.1
Gross Unrealized Losses	(0.5)	(0.7)
Amortized Cost	895.5	1,075.7
Government securities Non-current
Marketable Debt and Equity Securities
Fair Value	248.2	844.2
Gross Unrealized Gains	0.1	0.2
Gross Unrealized Losses	(0.3)	(1.1)
Amortized Cost	248.4	845.1
Mortgage and other asset backed securities Current
Marketable Debt and Equity Securities
Fair Value	0.1	0.8
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Amortized Cost	0.1	0.8
Mortgage and other asset backed securities Non-current
Marketable Debt and Equity Securities
Fair Value	307.0	642.6
Gross Unrealized Gains	0.1	1.1
Gross Unrealized Losses	(1.0)	(0.8)
Amortized Cost	$ 307.9	642.3
Marketable equity securities
Marketable Debt and Equity Securities
Fair Value		11.8
Gross Unrealized Gains		1.8
Gross Unrealized Losses		(4.4)
Amortized Cost		$ 14.4

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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