Income Taxes (Schedule Of Impacts Of the Tax Cuts and Jobs Act of 2017) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Income Tax [Line Items]
Other current assets	$ 0.0
Investments, ATC Investment	(75.0)
Other assets, regulatory assets	(387.6)
Other assets, deferred charges and other	41.0
Total Tax Reform impact on assets	(421.6)
Other liabilities, deferred tax liabilities	(1,331.9)
Other liabilities, regulatory liabilities	885.9
Other liabilities, other	6.3
Total Tax Reform impact on liabilities	(439.7)
Income tax expense (benefit)	(18.1)
IPL [Member]
Income Tax [Line Items]
Other current assets	4.7
Investments, ATC Investment	0.0
Other assets, regulatory assets	(375.0)
Other assets, deferred charges and other	0.0
Total Tax Reform impact on assets	(370.3)
Other liabilities, deferred tax liabilities	(757.2)
Other liabilities, regulatory liabilities	390.7
Other liabilities, other	0.0
Total Tax Reform impact on liabilities	(366.5)
Income tax expense (benefit)	3.8
WPL [Member]
Income Tax [Line Items]
Other current assets	(1.4)
Investments, ATC Investment	0.0
Other assets, regulatory assets	(12.7)
Other assets, deferred charges and other	0.0
Total Tax Reform impact on assets	(14.1)
Other liabilities, deferred tax liabilities	(523.8)
Other liabilities, regulatory liabilities	495.2
Other liabilities, other	0.0
Total Tax Reform impact on liabilities	(28.6)
Income tax expense (benefit)	$ (14.5)