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MATERIALS, SUPPLIES, AND INVENTORIES (Details) - USD ($) $ in Millions | Mar. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Materials, supplies, and inventories |  |
Natural gas in storage | $ 45.8 | $ 223.1
Materials and supplies | 208.3 | 206.5
Fossil fuel | 163.0 | 158.0
Total | 417.1 | $ 587.6
PGL and NSG |  |
Materials, supplies, and inventories |  |
Temporary LIFO liquidation debit | $ 31.6 |

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