Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Income Taxes [Line Items]
Income tax benefit, Federal Tax Reform	$ 5.6
Increase in deferred tax liabilities		$ 96.8
IPL [Member]
Income Taxes [Line Items]
Income tax benefit, Federal Tax Reform	1.1
Increase in deferred tax liabilities		22.3
WPL [Member]
Income Taxes [Line Items]
Income tax benefit, Federal Tax Reform	$ 5.5
Increase in deferred tax liabilities		$ 57.2