|
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]
|
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| 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]
|
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| 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]
|
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| Summary of financial assets with original maturities of less than 90 days included within cash and cash equivalents | ||
| Cash equivalents | $ 184.0 | $ 391.0 |