Debt (Summary of Cash Convertible Notes) (Details) (Cash Convertible Notes, USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Sep. 15, 2008
Convertible Debt
Debt Instrument [Line Items]
Outstanding principal	$ 574.0	$ 574.0	$ 575.0
Equity component carrying amount	1,650.3	1,303.3
Unamortized discount	(35.5)	(49.0)
Net debt carrying amount	2,188.8	1,828.3
Call Options
Debt Instrument [Line Items]
Purchased call options	$ 1,650.3	$ 1,303.3