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Litigation (Details) - USD ($) $ in Millions | Sep. 30, 2021 | Dec. 31, 2020 | Sep. 30, 2020
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Loss Contingencies [Line Items] |  |  |
Potential liabilities related to litigation and environmental matters | $ 34.7 | $ 41.5 | $ 72.7
Insurance Receivable | 11.7 | 17.5 | 49.1
Regulatory Assets | $ 21.1 | $ 21.3 | $ 20.9

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