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Commitments and Contingencies - MarkWest Environmental Proceeding (Details) - Pending Litigation - MarkWest Liberty Midstream Pipeline Launcher/Receiver Site [Member] $ in Millions | 3 Months Ended
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Mar. 31, 2017 USD ($)
Cash |
Loss Contingencies [Line Items] |
Alleged amount overcharged from customers | $ 2.4
Other Liabilities |
Loss Contingencies [Line Items] |
Alleged amount overcharged from customers | $ 3.6

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