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Fair Value Measurements (Details) (USD $)
In Millions, unless otherwise specified |
Mar. 31, 2012
Fair Value, Measurements, Recurring [Member]
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Dec. 31, 2011
Fair Value, Measurements, Recurring [Member]
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Dec. 31, 2011
Fair Value, Measurements, Nonrecurring [Member]
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Mar. 31, 2012
Fair Value, Inputs, Level 1 [Member]
Fair Value, Measurements, Recurring [Member]
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Dec. 31, 2011
Fair Value, Inputs, Level 1 [Member]
Fair Value, Measurements, Recurring [Member]
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Mar. 31, 2012
Fair Value, Inputs, Level 2 [Member]
Fair Value, Measurements, Recurring [Member]
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Dec. 31, 2011
Fair Value, Inputs, Level 2 [Member]
Fair Value, Measurements, Recurring [Member]
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Dec. 31, 2011
Fair Value, Inputs, Level 2 [Member]
Fair Value, Measurements, Nonrecurring [Member]
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Jul. 02, 2011
Fair Value, Inputs, Level 2 [Member]
Fair Value, Measurements, Nonrecurring [Member]
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Mar. 31, 2012
Fair Value, Inputs, Level 3 [Member]
Fair Value, Measurements, Recurring [Member]
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Dec. 31, 2011
Fair Value, Inputs, Level 3 [Member]
Fair Value, Measurements, Recurring [Member]
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|---|---|---|---|---|---|---|---|---|---|---|---|
| Assets: | |||||||||||
| Cash equivalents | $ 121.0 | $ 135.2 | $ 121.0 | $ 135.2 | $ 0 | $ 0 | $ 0 | $ 0 | |||
| Short-term investments in marketable securities | 63.9 | 76.7 | 3.1 | 5.5 | 60.8 | 71.2 | 0 | 0 | |||
| Long-term investments in marketable securities | 55.9 | 92.9 | 55.9 | 92.9 | 0 | 0 | 0 | 0 | |||
| Restricted cash | 20.0 | 20.0 | 20.0 | 20.0 | 0 | 0 | 0 | 0 | |||
| Equity investments | 0.4 | 0.7 | 0.4 | 0.7 | 0 | 0 | 0 | 0 | |||
| Derivatives | 1.4 | 3.9 | 0 | 0 | 1.4 | 3.9 | 0 | 0 | |||
| Total assets | 262.6 | 329.4 | 200.4 | 254.3 | 62.2 | 75.1 | 0 | 0 | |||
| Liabilities: | |||||||||||
| Derivatives | 7.1 | 8.0 | 0 | 0 | 7.1 | 8.0 | 0 | 0 | |||
| Total liabilities | 7.1 | 8.0 | 0 | 0 | 7.1 | 8.0 | 0 | 0 | |||
| Assets Measured at fair value on a non-recurring basis [Abstract] | |||||||||||
| Assets measured at fair value on a nonrecurring basis | $ 5.5 | $ 4.7 | $ 0.8 |