Income Taxes (Schedule Of Components Of Income Tax) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current tax expense (benefit):
Federal	$ 36.6	$ 4.4	$ (29.3)
State	9.3	(3.6)	11.6
Deferred tax expense (benefit):
Federal	83.5	123.9	157.8
State	4.6	15.6	23.9
Production tax credits	(31.3)	(31.0)	(24.8)
Investment tax credits	(1.6)	(1.6)	(1.7)
Provision recorded as a change in uncertain tax positions, current	0	0	8.0
Provision recorded as a change in uncertain tax positions, deferred	0	(0.4)	(7.6)
Provision recorded as a change in accrued interest	(0.1)	(0.5)	(0.2)
Income tax expense (benefit)	44.3	53.9	89.4
IPL's tax benefit riders [Member]
Current tax expense (benefit):
IPL's tax benefit riders	(56.7)	(52.9)	(48.3)
IPL [Member]
Current tax expense (benefit):
Federal	11.3	11.7	(7.7)
State	3.4	(0.1)	9.1
Deferred tax expense (benefit):
Federal	11.1	20.0	37.4
State	(6.2)	(0.8)	3.2
Production tax credits	(14.0)	(14.4)	(12.5)
Investment tax credits	(0.6)	(0.6)	(0.6)
Provision recorded as a change in uncertain tax positions, current	0	0	8.1
Provision recorded as a change in uncertain tax positions, deferred	0	0	(8.2)
Provision recorded as a change in accrued interest	0	(0.8)	(0.3)
Income tax expense (benefit)	(51.7)	(37.9)	(19.8)
IPL [Member] | IPL's tax benefit riders [Member]
Current tax expense (benefit):
IPL's tax benefit riders	(56.7)	(52.9)	(48.3)
WPL [Member]
Current tax expense (benefit):
Federal	0.6	(5.7)	7.2
State	4.4	6.0	(0.9)
Deferred tax expense (benefit):
Federal	88.9	92.7	81.1
State	10.1	11.8	20.3
Production tax credits	(17.3)	(16.6)	(12.3)
Investment tax credits	(1.0)	(1.0)	(1.1)
Provision recorded as a change in uncertain tax positions, current	0	0	(0.1)
Provision recorded as a change in uncertain tax positions, deferred	0	(0.4)	0.6
Provision recorded as a change in accrued interest	(0.1)	0.4	(0.2)
Income tax expense (benefit)	$ 85.6	$ 87.2	$ 94.6