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Inventory | 12 Months Ended
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Dec. 31, 2017
Inventory Disclosure [Abstract] |
INVENTORY | INVENTORY Inventory is valued primarily using the average-cost method. The following table summarizes the Company's inventory balances as of the dates indicated (in millions):
December 31, |  | 2017 |  | 2016
Fuel and other raw materials |  | $ | 284 |  |  | $ | 302 |
Spare parts and supplies |  | 278 |  |  | 320 |
Total |  | $ | 562 |  |  | $ | 622 |

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- Definition The entire disclosure for inventory. Includes, but is not limited to, the basis of stating inventory, the method of determining inventory cost, the classes of inventory, and the nature of the cost elements included in inventory. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 330 -URI http://asc.fasb.org/topic&trid=2126998 + Details
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