Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Marketable Debt and Equity Securities
Fair Value	$ 1,155.8	$ 1,245.9
Gross Unrealized Gains	0.7	0.4
Gross Unrealized Losses	(0.5)	(0.3)
Amortized Cost	1,155.6	1,245.8
Corporate debt securities Current
Marketable Debt and Equity Securities
Fair Value	135.7	100.7
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Amortized Cost	135.7	100.7
Corporate debt securities Non-current
Marketable Debt and Equity Securities
Fair Value	401.2	339.1
Gross Unrealized Gains	0.5	0.4
Gross Unrealized Losses	(0.2)	(0.1)
Amortized Cost	400.9	338.8
Government securities Current
Marketable Debt and Equity Securities
Fair Value	295.9	519.5
Gross Unrealized Gains	0.1	0
Gross Unrealized Losses	0	0
Amortized Cost	295.8	519.5
Government securities Non-current
Marketable Debt and Equity Securities
Fair Value	170.8	155.2
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(0.1)	(0.1)
Amortized Cost	170.9	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	152.2	131.4
Gross Unrealized Gains	0.1	0
Gross Unrealized Losses	(0.2)	(0.1)
Amortized Cost	152.3	131.5
Marketable equity securities
Marketable Debt and Equity Securities
Fair Value	13.8	11.2
Gross Unrealized Gains	11.4	8.7
Gross Unrealized Losses	(0.1)	0
Amortized Cost	$ 2.5	$ 2.5