Common Equity (Narrative) (Details) $ / shares in Units, $ in Millions		12 Months Ended
	Apr. 20, 2016 shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) $ / shares shares		Dec. 31, 2015 USD ($) shares		Dec. 31, 2014 USD ($) shares
Schedule of Common Equity [Line Items]
Common stock split conversion ratio (2:1)	2
Common stock, shares authorized (in shares) | shares	240,000,000			480,000,000	[1]	480,000,000	[1]
Shares available for issuance under the Amended and Restated OIP, Shareowner Direct Plan and 401(k) Savings Plan (in shares) | shares				11,300,000.0
Proceeds from issuance of common stock, net				$ 26.6		$ 151.2	[2]	$ 0.0
Ownership percentage				15.00%
Initial right entitlement, number of shares of common stock shareholders have the option to purchase (in shares) | shares				0.25
Exercise price, rights (in dollars per share) | $ / shares				$ 55.00
Percentage of exercise price upon change in beneficial ownership				200.00%
Other comprehensive income (loss)				$ 0.0		$ 0.2		(0.4)
IPL [Member]
Schedule of Common Equity [Line Items]
Common stock, shares authorized (in shares) | shares				24,000,000		24,000,000
Retained earnings free of dividend restrictions				$ 618.0
Common equity ratio, computation of ratio average, number of months				13 months
Common equity ratio				42.00%
Restricted net assets of subsidiaries				$ 1,600.0
Other comprehensive income (loss)				$ 0.0		$ 0.0		0.0
WPL [Member]
Schedule of Common Equity [Line Items]
Common stock, shares authorized (in shares) | shares				18,000,000		18,000,000
Retained earnings free of dividend restrictions				$ 126.0
Common equity ratio, computation of ratio average, number of months				13 months
Restricted net assets of subsidiaries				$ 1,600.0
Other comprehensive income (loss)				$ 0.0		$ 0.0		$ 0.0
Minimum [Member]
Schedule of Common Equity [Line Items]
Ownership percentage				10.00%
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						$ 150.0
Common stock issued during the period, At-the-market offering program (in shares) | shares				0		4,373,234		0
Proceeds from issuance of common stock, net						$ 133.0
Fees and commissions from issuance of common stock						$ 2.0
Scenario, Forecast [Member] | WPL [Member]
Schedule of Common Equity [Line Items]
Retained earnings free of dividend restrictions		$ 140.0	$ 126.0
Common equity ratio		51.00%	51.00%

[1] Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.

[2] Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.