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Leases (Finance Lease) (Details) - WPL [Member] - Sheboygan Falls Energy Facility [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases [Line Items]
Finance lease assets, Property, plant and equipment, net	$ 27	$ 32
Finance lease liabilities, Other current liabilities	9	9
Finance lease liabilities, Sheboygan Falls Energy Facility	42	51
Finance lease liabilities, Total	$ 51	$ 60
Finance lease, Remaining lease term	4 years	5 years
Finance lease, Discount rate, percent	11.00%	11.00%
Finance lease, Depreciation expense	$ 6	$ 6
Finance lease, Interest expense	6	7
Finance lease, Total expense	$ 12	$ 13

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