Financial Instruments (Details 1) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Marketable Debt and Equity Securities
Fair Value	$ 5,172.5	$ 5,398.0
Gross Unrealized Gains	2.3	2.9
Gross Unrealized Losses	(2.8)	(11.2)
Amortized Cost	5,173.0	5,406.3
Corporate debt securities Current
Marketable Debt and Equity Securities
Fair Value	1,039.3	1,408.6
Gross Unrealized Gains	0.0	0.2
Gross Unrealized Losses	(0.2)	(0.6)
Amortized Cost	1,039.5	1,409.0
Corporate debt securities Non-current
Marketable Debt and Equity Securities
Fair Value	1,570.5	1,255.2
Gross Unrealized Gains	0.9	1.2
Gross Unrealized Losses	0.0	(4.7)
Amortized Cost	1,569.6	1,258.7
Government securities Current
Marketable Debt and Equity Securities
Fair Value	1,075.1	1,156.0
Gross Unrealized Gains	0.1	0.2
Gross Unrealized Losses	(0.7)	(0.3)
Amortized Cost	1,075.7	1,156.1
Government securities Non-current
Marketable Debt and Equity Securities
Fair Value	844.2	1,016.5
Gross Unrealized Gains	0.2	0.5
Gross Unrealized Losses	(1.1)	(3.4)
Amortized Cost	845.1	1,019.4
Mortgage and other asset backed securities Current
Marketable Debt and Equity Securities
Fair Value	0.8	4.0
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Amortized Cost	0.8	4.0
Mortgage and other asset backed securities Non-current
Marketable Debt and Equity Securities
Fair Value	642.6	557.7
Gross Unrealized Gains	1.1	0.8
Gross Unrealized Losses	(0.8)	(2.2)
Amortized Cost	642.3	559.1
Marketable equity securities
Marketable Debt and Equity Securities
Fair Value	11.8	24.9
Gross Unrealized Gains	1.8	0.7
Gross Unrealized Losses	(4.4)	(9.3)
Amortized Cost	$ 14.4	$ 33.5