Acquired Sales Contracts (Narrative) (Details) (USD $) In Millions	6 Months Ended
Jun. 30, 2011
Coal supply agreement asset, purchase price allocation	$ 43.3
Coal supply agreement liability, purchase price allocation	121.0
Amortization expense (income) of acquired sales contracts year one	41.0
Amortization expense (income) of acquired sales contracts year two	10.0
Amortization expense (income) of acquired sales contracts year three	6.0
Amortization expense (income) of acquired sales contracts year four	9.0
Amortization expense (income) of acquired sales contracts year five	13.0
Current Asset [Member]
Business acquisition current assets	22.7
Current Liabilities [Member]
Business acquisition current liabilities	$ 75.4

Coal Supply Agreement Asset, Purchase Price Allocation

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Coal Supply Agreement Liability, Purchase Price Allocation

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The amount of acquisition cost of a business combination allocated to current assets.

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The amount of acquisition cost of a business combination allocated to current liabilities of the acquired entity.

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-Name Statement of Financial Accounting Standard (FAS)
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The amount of amortization expense expected to be recognized during year five of the five succeeding fiscal years.

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The amount of amortization expense expected to be recognized during year one of the five succeeding fiscal years.

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