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Regulatory Matters (Rate Case Action) (Details) - USD ($) $ in Millions | May 15, 2020 | Apr. 24, 2020 | Oct. 31, 2018
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NIPSCO - Electric |  |  |
Rate Case Action [Line Items] |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  | $ 21.4
Public Utilities, Approved Rate Increase (Decrease), Amount |  |  | $ (53.5)
Columbia Of Maryland |  |  |
Rate Case Action [Line Items] |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount | $ 5.0 |  |
Public Utilities, Approved Rate Increase (Decrease), Amount | $ 2.0 |  |
Columbia Of Pennsylvania |  |  |
Rate Case Action [Line Items] |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  | $ 100.4 |

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