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Related Parties (Narrative) (Details) - USD ($) $ in Millions | Mar. 31, 2024 | Dec. 31, 2023
--- | --- | ---
WPL [Member] | WPL Owed ATC LLC [Member] | Related Party [Member] |  |
Related Party Transactions [Line Items] |  |
Net amounts owed | $ 10 | $ 10

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