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Common Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Schedule of Common Equity [Line Items] |  |  |  |
Shares available for issuance under the Amended and Restated OIP, Shareowner Direct Plan and 401(k) Savings Plan (in shares) |  | 11,200,000.0 |  |
Proceeds from issuance of common stock, net |  | $ 196.6 | $ 149.6 | $ 26.6
Initial forward sale price (in dollars per share) |  | $ 44.33 |  |
Ownership percentage |  | 15.00% |  |
Other comprehensive income (loss) |  | $ 2.2 | (0.1) | 0.0
IPL [Member] |  |  |  |
Schedule of Common Equity [Line Items] |  |  |  |
Other comprehensive income (loss) |  | 0.0 | 0.0 | 0.0
WPL [Member] |  |  |  |
Schedule of Common Equity [Line Items] |  |  |  |
Other comprehensive income (loss) |  | 0.0 | 0.0 | $ 0.0
At The Market Offering Program [Member] |  |  |  |
Schedule of Common Equity [Line Items] |  |  |  |
Maximum aggregate gross sales price of common stock that can be offered and sold |  | $ 175.0 | $ 125.0 |
Common stock issued during the period, At-the-market offering programs (in shares) |  | 4,171,013 | 3,074,931 | 0
Proceeds from issuance of common stock, net |  | $ 173.0 | $ 124.0 |
Fees and commissions from issuance of common stock |  | $ 2.0 | $ 1.0 |
Scenario, Forecast [Member] |  |  |  |
Schedule of Common Equity [Line Items] |  |  |  |
Common stock issued during the period, At-the-market offering programs (in shares) | 8,358,973 |  |  |

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