Income Taxes (Schedule Of Components Of Income Tax) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current tax expense (benefit):
Federal	$ 2.0	$ 36.6	$ 4.4
State	3.2	9.3	(3.6)
Deferred tax expense (benefit):
Federal	120.8	83.5	123.9
State	27.9	4.6	15.6
Production tax credits	(33.1)	(31.3)	(31.0)
Investment tax credits	(1.4)	(1.6)	(1.6)
Provision recorded as a change in uncertain tax positions, deferred	0.0	0.0	(0.4)
Provision recorded as a change in accrued interest	0.0	(0.1)	(0.5)
Income tax expense (benefit)	70.4	44.3	53.9
IPL's tax benefit riders [Member]
Current tax expense (benefit):
IPL's tax benefit riders	(49.0)	(56.7)	(52.9)
IPL [Member]
Current tax expense (benefit):
Federal	(14.1)	8.9	10.2
State	11.5	10.4	4.2
Deferred tax expense (benefit):
Federal	40.7	10.8	21.7
State	3.3	(7.9)	(4.0)
Production tax credits	(14.5)	(13.8)	(14.1)
Investment tax credits	(0.6)	(0.6)	(0.6)
Provision recorded as a change in uncertain tax positions, deferred	0.0	0.0	0.0
Provision recorded as a change in accrued interest	0.0	0.0	(0.8)
Income tax expense (benefit)	(22.7)	(48.9)	(36.3)
IPL [Member] | IPL's tax benefit riders [Member]
Current tax expense (benefit):
IPL's tax benefit riders	(49.0)	(56.7)	(52.9)
WPL [Member]
Current tax expense (benefit):
Federal	4.7	2.0	(0.3)
State	0.6	0.8	(4.3)
Deferred tax expense (benefit):
Federal	76.8	81.1	84.0
State	20.2	20.0	24.1
Production tax credits	(18.6)	(17.5)	(16.9)
Investment tax credits	(0.8)	(1.0)	(1.0)
Provision recorded as a change in uncertain tax positions, deferred	0.0	0.0	(0.4)
Provision recorded as a change in accrued interest	0.0	(0.1)	0.4
Income tax expense (benefit)	$ 82.9	$ 85.3	$ 85.6