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Supplemental Coal Data (Unaudited) (Tables)
 12 Months Ended
Dec. 31, 2014
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,
 
 
2014

 
2013

 
2012

 
2011

 
2010

Proved and probable reserves at beginning of period
 
3,032

 
4,229

 
4,314

 
4,229

 
4,350

Purchased reserves
 
—

 
1

 
—

 
6

 
4

Reserves sold in place
 
(233
)
 
(1,199
)
 
(155
)
 
—

 
(41
)
Production
 
(32
)
 
(55
)
 
(55
)
 
(62
)
 
(62
)
Revisions and other changes
 
471

 
56

 
125

 
141

 
(22
)
Consolidated proved and probable reserves at end of period*
 
3,238

 
3,032

 
4,229

 
4,314

 
4,229

 
 
 
 
 
 
 
 
 
 
 
Proportionate share of proved and probable reserves of unconsolidated equity affiliates (excluded from the table above)*
 
55

 
57

 
41

 
145

 
172

______________
* 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.