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Litigation (Details) - USD ($) $ in Millions | Mar. 31, 2021 | Dec. 31, 2020 | Mar. 31, 2020
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Loss Contingencies [Line Items] |  |  |
Potential liabilities related to litigation and environmental matters | $ 55.0 | $ 41.5 | $ 33.1
Insurance Receivable | 31.6 | 17.5 | 19.0
Regulatory Assets | $ 20.9 | $ 21.3 | $ 10.8

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