Income Taxes (Schedule Of Components Of Income Tax) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current tax expense (benefit):
Federal	$ (1.0)	$ (41.0)	$ 1.8
State	(5.1)	8.5	17.2
Deferred tax expense (benefit):
Federal	67.9	159.5	112.8
State	29.8	12.3	4.9
Production tax credits	(29.5)	(31.1)	(31.8)
Investment tax credits	(1.2)	(1.1)	(1.3)
Income tax expense (benefit)	47.7	66.7	59.4
IPL's tax benefit riders [Member]
Current tax expense (benefit):
IPL's tax benefit riders	(13.2)	(40.4)	(44.2)
IPL [Member]
Current tax expense (benefit):
Federal	14.9	(27.9)	(12.8)
State	(7.1)	1.6	15.5
Deferred tax expense (benefit):
Federal	9.5	72.5	59.1
State	7.3	(2.2)	(9.0)
Production tax credits	(14.0)	(14.1)	(14.0)
Investment tax credits	(0.6)	(0.4)	(0.5)
Income tax expense (benefit)	(3.2)	(10.9)	(5.9)
IPL [Member] | IPL's tax benefit riders [Member]
Current tax expense (benefit):
IPL's tax benefit riders	(13.2)	(40.4)	(44.2)
WPL [Member]
Current tax expense (benefit):
Federal	(9.2)	5.5	(22.3)
State	(4.4)	2.5	1.1
Deferred tax expense (benefit):
Federal	43.8	55.0	112.3
State	22.1	16.6	20.8
Production tax credits	(15.5)	(17.0)	(17.8)
Investment tax credits	(0.6)	(0.7)	(0.8)
Income tax expense (benefit)	$ 36.2	$ 61.9	$ 93.3