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MATERIALS, SUPPLIES, AND INVENTORIES (Tables) | 9 Months Ended
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Sep. 30, 2017
Inventory Disclosure [Abstract] |
Schedule of inventory | 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 |

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