Quarterly report pursuant to Section 13 or 15(d)

Goodwill And Other Intangible Assets And Liabilities (Schedule Of Finite-Lived Intangible Assets By Major Class) (Detail)

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Goodwill And Other Intangible Assets And Liabilities (Schedule Of Finite-Lived Intangible Assets By Major Class) (Detail) (USD $)
In Millions, unless otherwise specified
Jun. 30, 2012
Dec. 31, 2011
Finite-Lived Intangible Assets [Line Items]    
Definite lived intangible assets - Accumulated Amortization $ (56.8) $ (47.5)
Definite lived intangible assets - Gross Carrying Amount 194.7 194.5
Below-market sales contracts - Accumulated Amortization 152.2 164.8
Definite lived intangible assets - Net Carrying Amount 137.9 147.0
Below-market sales contracts - Gross Carrying Amount (296.7) (329.3)
Below-market sales contracts - Net Carrying Amount (144.5) (164.5)
Below-Market Sales Contracts Current [Member]
    
Finite-Lived Intangible Assets [Line Items]    
Below-market sales contracts - Accumulated Amortization   24.3
Below-market sales contracts - Gross Carrying Amount (46.0) (77.0)
Classification of intangible assets and liabilities Other current liabilities  
Below-market sales contracts - Net Carrying Amount (46.0) (52.7)
Below Market Sales Contracts [Member]
    
Finite-Lived Intangible Assets [Line Items]    
Below-market sales contracts - Accumulated Amortization 152.2 140.5
Below-market sales contracts - Gross Carrying Amount (250.7) (252.3)
Classification of intangible assets and liabilities Below-market sales contracts  
Below-market sales contracts - Net Carrying Amount (98.5) (111.8)
Permits [Member]
    
Finite-Lived Intangible Assets [Line Items]    
Definite lived intangible assets - Accumulated Amortization (26.8) (23.2)
Definite lived intangible assets - Gross Carrying Amount 134.5 134.3
Definite lived intangible assets - Net Carrying Amount 107.7 111.1
Classification of intangible assets and liabilities Intangible assets, net  
Utility Contracts [Member]
    
Finite-Lived Intangible Assets [Line Items]    
Definite lived intangible assets - Accumulated Amortization (26.9) (21.3)
Definite lived intangible assets - Gross Carrying Amount 54.7 54.7
Definite lived intangible assets - Net Carrying Amount 27.8 33.4
Classification of intangible assets and liabilities Intangible assets, net  
Leases [Member]
    
Finite-Lived Intangible Assets [Line Items]    
Definite lived intangible assets - Accumulated Amortization (3.1) (3.0)
Definite lived intangible assets - Gross Carrying Amount 5.5 5.5
Definite lived intangible assets - Net Carrying Amount $ 2.4 $ 2.5
Classification of intangible assets and liabilities Intangible assets, net