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

Amount of interest expense on finance lease liability.

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Present value of lessee's discounted obligation for lease payments from finance lease.

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Present value of lessee's discounted obligation for lease payments from finance lease, classified as current.

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Present value of lessee's discounted obligation for lease payments from finance lease, classified as noncurrent.

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Amount of lessee's right to use underlying asset under finance lease.

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Amount of amortization expense attributable to right-of-use asset from finance lease.

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Weighted average discount rate for finance lease calculated at point in time.

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Weighted average remaining lease term for finance lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of lease cost recognized by lessee for lease contract.

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