Income Taxes (Schedule Of Components Of Income Tax) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current tax expense (benefit):
Federal	$ (41.0)	$ 1.8	$ 2.0
State	8.5	17.2	3.2
Deferred tax expense (benefit):
Federal	159.5	112.8	120.8
State	12.3	4.9	27.9
Production tax credits	(31.1)	(31.8)	(33.1)
Investment tax credits	(1.1)	(1.3)	(1.4)
Income tax expense (benefit)	66.7	59.4	70.4
IPL's tax benefit riders [Member]
Current tax expense (benefit):
IPL's tax benefit riders	(40.4)	(44.2)	(49.0)
IPL [Member]
Current tax expense (benefit):
Federal	(27.9)	(12.8)	(14.1)
State	1.6	15.5	11.5
Deferred tax expense (benefit):
Federal	72.5	59.1	40.7
State	(2.2)	(9.0)	3.3
Production tax credits	(14.1)	(14.0)	(14.5)
Investment tax credits	(0.4)	(0.5)	(0.6)
Income tax expense (benefit)	(10.9)	(5.9)	(22.7)
IPL [Member] | IPL's tax benefit riders [Member]
Current tax expense (benefit):
IPL's tax benefit riders	(40.4)	(44.2)	(49.0)
WPL [Member]
Current tax expense (benefit):
Federal	5.5	(22.3)	4.7
State	2.5	1.1	0.6
Deferred tax expense (benefit):
Federal	55.0	112.3	76.8
State	16.6	20.8	20.2
Production tax credits	(17.0)	(17.8)	(18.6)
Investment tax credits	(0.7)	(0.8)	(0.8)
Income tax expense (benefit)	$ 61.9	$ 93.3	$ 82.9