Supplemental Coal Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2011

SUPPLEMENTAL COAL DATA [Abstract]

Reserves Reported to Other Agencies [Table Text Block]

Supplemental Coal Data (unaudited)

	Millions of Tons
	For the Year Ended December 31,
	2011		2010		2009		2008		2007
Proved and probable reserves at beginning of period....................................	4,401		4,520		4,543		4,526		4,272
Purchased reserves.........................................................................................	6		4		5		—		177
Reserves sold in place....................................................................................	—		(41	)	(3	)	(12	)	(33	)
Production......................................................................................................	(63	)	(63	)	(59	)	(65	)	(65	)
Revisions and other changes..........................................................................	115		(19	)	34		94		175
Consolidated proved and probable reserves at end of period*......................	4,459		4,401		4,520		4,543		4,526
Proportionate share of proved and probable reserves of unconsolidated equity affiliates*.........................................................................................	145		172		170		171		179

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* Proved and probable coal reserves are the equivalent of “demonstrated reserves” under the coal resource classification system of the U.S. Geological Survey. Generally, these reserves would be commercially mineable at year-end prices and cost levels, using current technology and mining practices.