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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Related Parties (Narrative) (Details) - ATC LLC [Member] - Equity Method Investee [Member] - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2020	Sep. 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