Debt (Summary of Cash Convertible Notes) (Details) (Cash Convertible Notes, USD $) In Millions, unless otherwise specified	Mar. 31, 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	1,535.1	1,303.3
Unamortized discount	(42.3)	(49.0)
Net debt carrying amount	2,066.8	1,828.3
Call Options
Debt Instrument [Line Items]
Purchased call options	$ 1,535.1	$ 1,303.3