Financial Instruments (Details 1) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	$ 309.0	$ 399.8
Commercial paper [Member]
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	16.3	0
Repurchase Agreements [Member]
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	108.7	8.8
Short-term Debt Securities [Member]
Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents
Cash equivalents	$ 184.0	$ 391.0