Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Marketable Debt and Equity Securities
Fair Value	$ 1,720.6	$ 1,245.9
Gross Unrealized Gains	1.1	0.4
Gross Unrealized Losses	(0.4)	(0.3)
Amortized Cost	1,719.9	1,245.8
Corporate debt securities Current
Marketable Debt and Equity Securities
Fair Value	125.0	100.7
Gross Unrealized Gains	0.1	0
Gross Unrealized Losses	0	0
Amortized Cost	124.9	100.7
Corporate debt securities Non-current
Marketable Debt and Equity Securities
Fair Value	492.2	339.1
Gross Unrealized Gains	0.6	0.4
Gross Unrealized Losses	(0.2)	(0.1)
Amortized Cost	491.8	338.8
Government securities Current
Marketable Debt and Equity Securities
Fair Value	584.9	519.5
Gross Unrealized Gains	0.1	0
Gross Unrealized Losses	(0.1)	0
Amortized Cost	584.9	519.5
Government securities Non-current
Marketable Debt and Equity Securities
Fair Value	363.1	155.2
Gross Unrealized Gains	0.2	0
Gross Unrealized Losses	0	(0.1)
Amortized Cost	362.9	155.3
Mortgage and other asset backed securities Current
Marketable Debt and Equity Securities
Fair Value	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Amortized Cost	0	0
Mortgage and other asset backed securities Non-current
Marketable Debt and Equity Securities
Fair Value	155.4	131.4
Gross Unrealized Gains	0.1	0
Gross Unrealized Losses	(0.1)	(0.1)
Amortized Cost	155.4	131.5
Marketable equity securities
Marketable Debt and Equity Securities
Fair Value	0.4	11.2
Gross Unrealized Gains	0	8.7
Gross Unrealized Losses	(0.1)	0
Amortized Cost	$ 0.5	$ 2.5