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MATERIALS, SUPPLIES, AND INVENTORIES (Details) - USD ($) $ in Millions | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Energy Related Inventory |  |
Natural gas in storage | $ 274.4 | $ 209.0
Materials and supplies | 227.5 | 211.2
Fossil fuel | 106.6 | 118.8
Total | 608.5 | $ 539.0
LIFO Method Related Items |  |
LIFO Liquidation Balance | $ 0.0 |

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- Definition Carrying amount as of the balance sheet date of merchandise, goods, commodities, or supplies relating to a source of usable power held for future sale or future use in manufacturing or production process. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.6(a)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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