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COMMITMENTS AND CONTINGENCIES (Details) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2018 | Dec. 31, 2017 USD ($) | Dec. 31, 2016
Commitments and Contingencies [Line Items] |  |  |
Number Of Former Manufactured Gas Sites Where We Own Or Retain Legal Responsibility For Environmental Conditions | 12 |  |
AAO associated with MGP costs requested amount, cap |  | $ 15.0 |
Regulatory asset expected to be recorded for MGP costs accrued at January 1, 2017 |  | $ 5.9 |
Number of sites where we have completed or addressed removal of the source of soil contamination according to plans approved by KDHE. | 11 |  |
Number of sites with ongoing groundwater monitoring | 8 |  |
Number of sites where regulatory closure has been achieved | 3 |  |
Environmental Reserve Estimate Range, Low | 5.6 |  | 4
Environmental Reserve Estimate Range, High | 7 |  | 7
Environmental Reserve Estimate, Actual | 1.6 |  |
Percentage yield of high consequence pipeline areas | 30.00% |  |

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