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Commitments and Contingencies (Details) $ in Millions | Sep. 30, 2020 USD ($) case | Jun. 30, 2019 facility
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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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