v2.4.0.6
Financial Instruments (Details 4) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Liabilities:    
Fair value of fuel and commodity hedges included in other accrued liabilities $ 1.8 $ 1.6
Fair Value, Measurements, Recurring [Member]
   
Assets:    
Total assets 109.9 107.0
Liabilities:    
Total liabilities 1.8 1.6
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets (Level 1) [Member]
   
Assets:    
Total assets 62.3 62.8
Liabilities:    
Total liabilities 0 0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
   
Assets:    
Total assets 47.6 44.2
Liabilities:    
Total liabilities 1.8 1.6
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
   
Assets:    
Total assets 0 0
Liabilities:    
Total liabilities 0 0
Fair Value, Measurements, Recurring [Member] | Commodity hedges [Member]
   
Assets:    
Other current assets 0.4 1.0
Liabilities:    
Fair value of fuel and commodity hedges included in other accrued liabilities 1.7 1.2
Fair Value, Measurements, Recurring [Member] | Commodity hedges [Member] | Quoted Prices in Active Markets (Level 1) [Member]
   
Assets:    
Other current assets 0 0
Liabilities:    
Fair value of fuel and commodity hedges included in other accrued liabilities 0 0
Fair Value, Measurements, Recurring [Member] | Commodity hedges [Member] | Significant Other Observable Inputs (Level 2) [Member]
   
Assets:    
Other current assets 0.4 1.0
Liabilities:    
Fair value of fuel and commodity hedges included in other accrued liabilities 1.7 1.2
Fair Value, Measurements, Recurring [Member] | Commodity hedges [Member] | Significant Unobservable Inputs (Level 3) [Member]
   
Assets:    
Other current assets 0 0
Liabilities:    
Fair value of fuel and commodity hedges included in other accrued liabilities 0 0
Fair Value, Measurements, Recurring [Member] | Fuel hedges [Member]
   
Assets:    
Other current assets 5.0 3.1
Liabilities:    
Fair value of fuel and commodity hedges included in other accrued liabilities 0.1 0.4
Fair Value, Measurements, Recurring [Member] | Fuel hedges [Member] | Quoted Prices in Active Markets (Level 1) [Member]
   
Assets:    
Other current assets 0 0
Liabilities:    
Fair value of fuel and commodity hedges included in other accrued liabilities 0 0
Fair Value, Measurements, Recurring [Member] | Fuel hedges [Member] | Significant Other Observable Inputs (Level 2) [Member]
   
Assets:    
Other current assets 5.0 3.1
Liabilities:    
Fair value of fuel and commodity hedges included in other accrued liabilities 0.1 0.4
Fair Value, Measurements, Recurring [Member] | Fuel hedges [Member] | Significant Unobservable Inputs (Level 3) [Member]
   
Assets:    
Other current assets 0 0
Liabilities:    
Fair value of fuel and commodity hedges included in other accrued liabilities 0 0
Fair Value, Measurements, Recurring [Member] | Money market mutual funds [Member]
   
Assets:    
Available-for-sale securities 62.3 62.8
Fair Value, Measurements, Recurring [Member] | Money market mutual funds [Member] | Quoted Prices in Active Markets (Level 1) [Member]
   
Assets:    
Available-for-sale securities 62.3 62.8
Fair Value, Measurements, Recurring [Member] | Money market mutual funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
   
Assets:    
Available-for-sale securities 0 0
Fair Value, Measurements, Recurring [Member] | Money market mutual funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
   
Assets:    
Available-for-sale securities 0 0
Fair Value, Measurements, Recurring [Member] | Bonds [Member]
   
Assets:    
Available-for-sale securities 42.2 40.1
Fair Value, Measurements, Recurring [Member] | Bonds [Member] | Quoted Prices in Active Markets (Level 1) [Member]
   
Assets:    
Available-for-sale securities 0 0
Fair Value, Measurements, Recurring [Member] | Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
   
Assets:    
Available-for-sale securities 42.2 40.1
Fair Value, Measurements, Recurring [Member] | Bonds [Member] | Significant Unobservable Inputs (Level 3) [Member]
   
Assets:    
Available-for-sale securities $ 0 $ 0