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Inventory
3 Months Ended
Mar. 31, 2012
INVENTORY

2. INVENTORY

The following table summarizes the Company's inventory balances as of March 31, 2012 and December 31, 2011:

  March 31, December 31,
  2012 2011
       
  (in millions)
Coal, fuel oil and other raw materials $ 432 $ 444
Spare parts and supplies   367   341
Total $ 799 $ 785