Financial Instruments (Details 1) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Fair value	$ 3,286.2	$ 5,172.5
Gross unrealized gains	0.7	2.3
Gross unrealized losses	(2.9)	(2.8)
Amortized cost	3,288.4	5,173.0
Corporate debt securities Current
Debt Securities, Available-for-sale [Line Items]
Fair value	1,273.7	1,039.3
Gross unrealized gains	0.1	0.0
Gross unrealized losses	(0.4)	(0.2)
Amortized cost	1,274.0	1,039.5
Corporate debt securities Non-current
Debt Securities, Available-for-sale [Line Items]
Fair value	677.9	1,570.5
Gross unrealized gains	0.5	0.9
Gross unrealized losses	(0.8)	0.0
Amortized cost	678.2	1,569.6
Government securities Current
Debt Securities, Available-for-sale [Line Items]
Fair value	767.9	1,075.1
Gross unrealized gains	0.0	0.1
Gross unrealized losses	(0.5)	(0.7)
Amortized cost	768.4	1,075.7
Government securities Non-current
Debt Securities, Available-for-sale [Line Items]
Fair value	293.0	844.2
Gross unrealized gains	0.0	0.2
Gross unrealized losses	(0.6)	(1.1)
Amortized cost	293.6	845.1
Mortgage and other asset backed securities Current
Debt Securities, Available-for-sale [Line Items]
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
Debt Securities, Available-for-sale [Line Items]
Fair value	273.6	642.6
Gross unrealized gains	0.1	1.1
Gross unrealized losses	(0.6)	(0.8)
Amortized cost	274.1	642.3
Marketable equity securities
Debt Securities, Available-for-sale [Line Items]
Marketable equity securities, fair value	624.8	11.8
Marketable equity securities, gross unrealized gains	132.6	1.8
Marketable equity securities, gross unrealized losses	(4.4)	(4.4)
Marketable equity securities, amortized cost	$ 496.6	$ 14.4

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
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