Income Taxes (Schedule Of Components Of Income Tax) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current tax expense (benefit):
Federal	$ 1.8	$ 2.0	$ 36.6
State	17.2	3.2	9.3
Deferred tax expense (benefit):
Federal	112.8	120.8	83.5
State	4.9	27.9	4.6
Production tax credits	(31.8)	(33.1)	(31.3)
Investment tax credits	(1.3)	(1.4)	(1.6)
Provision recorded as a change in accrued interest	0.0	0.0	(0.1)
Income tax expense (benefit)	59.4	70.4	44.3
IPL's tax benefit riders [Member]
Current tax expense (benefit):
IPL's tax benefit riders	(44.2)	(49.0)	(56.7)
IPL [Member]
Current tax expense (benefit):
Federal	(12.8)	(14.1)	8.9
State	15.5	11.5	10.4
Deferred tax expense (benefit):
Federal	59.1	40.7	10.8
State	(9.0)	3.3	(7.9)
Production tax credits	(14.0)	(14.5)	(13.8)
Investment tax credits	(0.5)	(0.6)	(0.6)
Provision recorded as a change in accrued interest	0.0	0.0	0.0
Income tax expense (benefit)	(5.9)	(22.7)	(48.9)
IPL [Member] | IPL's tax benefit riders [Member]
Current tax expense (benefit):
IPL's tax benefit riders	(44.2)	(49.0)	(56.7)
WPL [Member]
Current tax expense (benefit):
Federal	(22.3)	4.7	2.0
State	1.1	0.6	0.8
Deferred tax expense (benefit):
Federal	112.3	76.8	81.1
State	20.8	20.2	20.0
Production tax credits	(17.8)	(18.6)	(17.5)
Investment tax credits	(0.8)	(0.8)	(1.0)
Provision recorded as a change in accrued interest	0.0	0.0	(0.1)
Income tax expense (benefit)	$ 93.3	$ 82.9	$ 85.3