Acquired Sales Contracts (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Acquired Sales Contracts [Abstract]
Coal supply agreement asset, purchase price allocation	$ 35.0
Coal supply agreement liability, purchase price allocation	126.0
Amortization expense (income) of acquired sales contracts, year 2012	18.5
Amortization expense (income) of acquired sales contracts, year 2013	5.2
Amortization expense (income) of acquired sales contracts, year 2014	3.3
Amortization expense (income) of acquired sales contracts, year 2015	12.7
Amortization expense (income) of acquired sales contracts, year 2016	$ 7.7