Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Marketable Debt and Equity Securities
Fair Value	$ 614.4	$ 3,171.7
Gross Unrealized Gains	0.3	5.6
Gross Unrealized Losses	0.3	1.9
Amortized Cost	614.4	3,168.0
Corporate debt securities Current [Member]
Marketable Debt and Equity Securities
Fair Value	76.7	346.9
Gross Unrealized Gains	0	0.3
Gross Unrealized Losses	0	0
Amortized Cost	76.7	346.6
Corporate debt securities Non-current [Member]
Marketable Debt and Equity Securities
Fair Value	210.3	654.1
Gross Unrealized Gains	0.3	2.8
Gross Unrealized Losses	0.1	0.6
Amortized Cost	210.1	651.9
Government securities Current [Member]
Marketable Debt and Equity Securities
Fair Value	164.2	783.4
Gross Unrealized Gains	0	0.3
Gross Unrealized Losses	0	0
Amortized Cost	164.2	783.1
Government securities Non-current [Member]
Marketable Debt and Equity Securities
Fair Value	103.0	874.4
Gross Unrealized Gains	0	0.8
Gross Unrealized Losses	0.1	0
Amortized Cost	103.1	873.6
Mortgage and other asset backed securities Current [Member]
Marketable Debt and Equity Securities
Fair Value	0	4.8
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Amortized Cost	0	4.8
Mortgage and other asset backed securities Non-current [Member]
Marketable Debt and Equity Securities
Fair Value	60.2	508.1
Gross Unrealized Gains	0	1.4
Gross Unrealized Losses	0.1	1.3
Amortized Cost	60.3	508.0
Marketable equity securities [Member]
Marketable Debt and Equity Securities
Gross Unrealized Gains	24.3	3.0
Gross Unrealized Losses	0	0
Amortized Cost	16.0	6.0
Fair Value	$ 40.3	$ 9.0