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
Sep. 30, 2012
Dec. 31, 2011
Finite-Lived Intangible Assets [Line Items]    
Definite lived intangible assets - Gross Carrying Amount $ 195.5 $ 194.5
Definite lived intangible assets - Accumulated Amortization (61.7) (47.5)
Definite lived intangible assets - Net Carrying Amount 133.8 147.0
Below-market sales contracts - Gross Carrying Amount (296.7) (329.3)
Below-market sales contracts - Accumulated Amortization 166.9 164.8
Below-market sales contracts - Net Carrying Amount (129.8) (164.5)
Below-Market Sales Contracts Current [Member]
    
Finite-Lived Intangible Assets [Line Items]    
Below-market sales contracts - Gross Carrying Amount (46.0) (77.0)
Below-market sales contracts - Accumulated Amortization    24.3
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 - Gross Carrying Amount (250.7) (252.3)
Below-market sales contracts - Accumulated Amortization 166.9 140.5
Below-market sales contracts - Net Carrying Amount (83.8) (111.8)
Permits [Member]
    
Finite-Lived Intangible Assets [Line Items]    
Definite lived intangible assets - Gross Carrying Amount 135.3 134.3
Definite lived intangible assets - Accumulated Amortization (28.9) (23.2)
Definite lived intangible assets - Net Carrying Amount 106.4 111.1
Utility Contracts [Member]
    
Finite-Lived Intangible Assets [Line Items]    
Definite lived intangible assets - Gross Carrying Amount 54.7 54.7
Definite lived intangible assets - Accumulated Amortization (29.7) (21.3)
Definite lived intangible assets - Net Carrying Amount 25.0 33.4
Leases [Member]
    
Finite-Lived Intangible Assets [Line Items]    
Definite lived intangible assets - Gross Carrying Amount 5.5 5.5
Definite lived intangible assets - Accumulated Amortization (3.1) (3.0)
Definite lived intangible assets - Net Carrying Amount $ 2.4 $ 2.5