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Leases (Finance Lease) (Details) - WPL [Member] - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2019 | Jun. 30, 2019 | Dec. 31, 2018
Leases [Line Items] |  |  |
Finance lease liabilities, Sheboygan Falls Energy Facility | $ 55.8 | $ 55.8 | $ 60.0
Sheboygan Falls Energy Facility [Member] |  |  |
Leases [Line Items] |  |  |
Finance lease assets, Property, plant and equipment, net | 35.0 | 35.0 |
Finance lease liabilities, Other current liabilities | 8.0 | 8.0 |
Finance lease liabilities, Sheboygan Falls Energy Facility | 56.0 | 56.0 |
Finance lease liabilities, Total | $ 64.0 | $ 64.0 |
Finance Lease, Weighted Average Remaining Lease Term | 6 years | 6 years |
Finance lease, Discount rate, percent | 11.00% | 11.00% |
Finance lease, Depreciation expense | $ 2.0 | $ 3.0 |
Finance lease, Interest expense | 2.0 | 4.0 |
Finance lease, Total expense | $ 4.0 | $ 7.0 |

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