Common Equity (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Common Equity [Line Items]
Proceeds from issuance of common stock, net			$ 143.2	$ 20.4
Comprehensive income	$ 0.0	$ 0.0	0.0	0.0
IPL [Member]
Common Equity [Line Items]
Retained earnings free of dividend restrictions	701.0		701.0
Restricted net assets of subsidiaries	1,700.0		1,700.0
Comprehensive income	0.0	0.0	0.0	0.0
WPL [Member]
Common Equity [Line Items]
Retained earnings free of dividend restrictions	32.0		32.0
Restricted net assets of subsidiaries	1,800.0		1,800.0
Comprehensive income	$ 0.0	$ 0.0	0.0	$ 0.0
At-The-Market Offering Program [Member]
Common Equity [Line Items]
Maximum aggregate gross sales price of common stock that can be offered and sold			$ 125.0
At-the-market offering program issuances (in shares)			3,074,931
Proceeds from issuance of common stock, net			$ 124.0
Commissions and fees from issuance of common stock			$ 1.0