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MATERIALS, SUPPLIES, AND INVENTORIES | 9 Months Ended
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Sep. 30, 2017
Inventory Disclosure [Abstract] |
MATERIALS, SUPPLIES, AND INVENTORIES | MATERIALS, SUPPLIES, AND INVENTORIES Our inventory consisted of:
(in millions) |  | September 30, 2017 |  | December 31, 2016
Natural gas in storage |  | $ | 301.5 |  |  | $ | 223.1 |
Materials and supplies |  | 225.1 |  |  | 206.5 |
Fossil fuel |  | 145.6 |  |  | 158.0 |
Total |  | $ | 672.2 |  |  | $ | 587.6 |
PGL and NSG price natural gas storage injections at the calendar year average of the cost of natural gas supply purchased. Withdrawals from storage are priced using the LIFO cost method. For interim periods, the difference between current projected replacement cost and the LIFO cost for quantities of natural gas temporarily withdrawn from storage is recorded as a temporary LIFO liquidation debit or credit. At September 30, 2017, all LIFO layers were replenished, and the LIFO liquidation balance was zero. Substantially all other natural gas in storage, materials and supplies, and fossil fuel inventories are recorded using the weighted-average cost method of accounting.

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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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