Related Parties (Narrative) (Details) - ATC LLC [Member] - Equity Method Investee [Member] - USD ($) $ in Millions	3 Months Ended
Jun. 30, 2020	Dec. 31, 2019
WPL Owed ATC LLC [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 9	$ 9
WPL [Member]
Related Party Transactions [Line Items]
Receipt of construction deposits	$ 46

The cash inflow from borrowing by the entity from developers, builders, government agencies and municipalities for construction that are repaid in cash, generally on a straight-line basis over periods ranging from five to forty years.

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-Name Accounting Standards Codification
-Topic 230
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Receivables to be collected from (obligations owed to) related parties, net as of the balance sheet date where one party can exercise control or significant influence over another party; including affiliates, owners or officers and their immediate families, pension trusts, and so forth.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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