Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 years	Dec. 31, 2010
Accounting Policies [Line Items]
Company's membership interest percentage in joint venture	99.00%
Number of mining complexes operated	23
Net book value of leased coal interests	$ 10,868,694,000	$ 5,792,945,000
Minimum useful lives lease agreements	10
Minimum useful lives lease agreements	50
Incurred financing fees	90,500,000	37,600,000
Unamortized deferred financing costs, current	15,800,000	9,600,000
Buildings And Leasehold Improvements [Member]
Accounting Policies [Line Items]
Minimum useful life of mining equipment	10
Maximum useful life of mining equipment	30
Exploration And Production Equipment [Member]
Accounting Policies [Line Items]
Minimum useful life of mining equipment	5
Maximum useful life of mining equipment	32
Mining Properties And Mineral Rights [Member]
Accounting Policies [Line Items]
Net book value of leased coal interests	$ 1,600,000,000	$ 1,600,000,000