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Commitments and Contingencies (Details) $ in Millions | Mar. 31, 2020 case | Dec. 31, 2018 facility | Aug. 18, 2016 USD ($)
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Sierra Club Et Al V. Midwest Generation LLC |  |  |
Loss Contingencies |  |  |
Number of facilities | facility |  | 4 |
XOOM Energy Litigation |  |  |
Loss Contingencies |  |  |
Pending lawsuits | case | 2 |  |
Lignite Contract With Texas Westmoreland Coal Co. |  |  |
Loss Contingencies |  |  |
Bond obligation | $ |  |  | $ 99

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