Financial Instruments (Details 1) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Marketable Debt and Equity Securities
Fair Value	$ 5,022.2	$ 5,398.0
Gross Unrealized Gains	4.1	2.9
Gross Unrealized Losses	(8.1)	(11.2)
Amortized Cost	5,026.2	5,406.3
Corporate debt securities Current
Marketable Debt and Equity Securities
Fair Value	1,042.9	1,408.6
Gross Unrealized Gains	0.2	0.2
Gross Unrealized Losses	(0.4)	(0.6)
Amortized Cost	1,043.1	1,409.0
Corporate debt securities Non-current
Marketable Debt and Equity Securities
Fair Value	1,541.8	1,255.2
Gross Unrealized Gains	2.2	1.2
Gross Unrealized Losses	(2.1)	(4.7)
Amortized Cost	1,541.7	1,258.7
Government securities Current
Marketable Debt and Equity Securities
Fair Value	916.0	1,156.0
Gross Unrealized Gains	0.0	0.2
Gross Unrealized Losses	(0.8)	(0.3)
Amortized Cost	916.8	1,156.1
Government securities Non-current
Marketable Debt and Equity Securities
Fair Value	954.0	1,016.5
Gross Unrealized Gains	0.4	0.5
Gross Unrealized Losses	(3.4)	(3.4)
Amortized Cost	957.0	1,019.4
Mortgage and other asset backed securities Current
Marketable Debt and Equity Securities
Fair Value	1.3	4.0
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Amortized Cost	1.3	4.0
Mortgage and other asset backed securities Non-current
Marketable Debt and Equity Securities
Fair Value	566.2	557.7
Gross Unrealized Gains	1.3	0.8
Gross Unrealized Losses	(1.4)	(2.2)
Amortized Cost	566.3	559.1
Marketable equity securities
Marketable Debt and Equity Securities
Fair Value	11.8	24.9
Gross Unrealized Gains	0.0	0.7
Gross Unrealized Losses	(2.6)	(9.3)
Amortized Cost	$ 14.4	$ 33.5