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