Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Deferred tax liabilities, gross	$ 2,647.7	$ 2,507.0
Deferred tax assets, valuation allowance	0	1.9
Deferred tax assets, net of valuation allowance	671.7	743.0
Deferred tax liabilities, net of deferred tax assets and valuation allowance	1,976.0	1,764.0
Current deferred tax assets	(136.7)	(170.2)
Non-current deferred tax liabilities	2,112.7	1,934.2
IPL [Member]
Deferred tax assets, gross	(336.0)	(383.4)
Deferred tax liabilities, gross	1,441.3	1,391.4
Deferred tax assets and liabilities, net	1,105.3	1,008.0
Deferred tax liabilities, net of deferred tax assets and valuation allowance	1,105.3	1,008.0
Current deferred tax assets	(87.7)	(79.3)
Non-current deferred tax liabilities	1,193.0	1,087.3
WPL [Member]
Deferred tax assets, gross	(201.6)	(222.8)
Deferred tax liabilities, gross	1,055.4	981.3
Deferred tax assets and liabilities, net	853.8	758.5
Deferred tax liabilities, net of deferred tax assets and valuation allowance	853.8	758.5
Current deferred tax assets	(43.3)	(85.6)
Non-current deferred tax liabilities	897.1	844.1
Property [Member]
Deferred tax assets, gross	0	0
Deferred tax liabilities, gross	2,316.3	2,143.8
Deferred tax assets and liabilities, net	2,316.3	2,143.8
Property [Member] | IPL [Member]
Deferred tax assets, gross	0	0
Deferred tax liabilities, gross	1,338.1	1,243.9
Deferred tax assets and liabilities, net	1,338.1	1,243.9
Property [Member] | WPL [Member]
Deferred tax assets, gross	0	0
Deferred tax liabilities, gross	859.1	793.3
Deferred tax assets and liabilities, net	859.1	793.3
Investment In ATC [Member]
Deferred tax assets, gross	0	0
Deferred tax liabilities, gross	120.7	104.3
Deferred tax assets and liabilities, net	120.7	104.3
Investment In ATC [Member] | WPL [Member]
Deferred tax assets, gross	0	0
Deferred tax liabilities, gross	120.7	104.3
Deferred tax assets and liabilities, net	120.7	104.3
Net operating losses carryforward - state [Member]
Deferred tax assets, gross	(35.3)	(46.8)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(35.3)	(46.8)
Regulatory liability - IPL's tax benefit riders [Member]
Deferred tax assets, gross	(107.8)	(144.6)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(107.8)	(144.6)
Regulatory liability - IPL's tax benefit riders [Member] | IPL [Member]
Deferred tax assets, gross	(107.8)	(144.6)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(107.8)	(144.6)
Federal credit carryforward [Member]
Deferred tax assets, gross	(167.8)	(133.8)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(167.8)	(133.8)
Federal credit carryforward [Member] | IPL [Member]
Deferred tax assets, gross	(52.9)	(37.4)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(52.9)	(37.4)
Federal credit carryforward [Member] | WPL [Member]
Deferred tax assets, gross	(57.1)	(39.4)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(57.1)	(39.4)
Net operating losses carryforward - federal [Member]
Deferred tax assets, gross	(251.9)	(306.0)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(251.9)	(306.0)
Net operating losses carryforward - federal [Member] | IPL [Member]
Deferred tax assets, gross	(111.3)	(131.0)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(111.3)	(131.0)
Net operating losses carryforward - federal [Member] | WPL [Member]
Deferred tax assets, gross	(106.9)	(142.2)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(106.9)	(142.2)
Other [Member]
Deferred tax assets, gross	(108.9)	(113.7)
Deferred tax liabilities, gross	210.7	258.9
Deferred tax assets and liabilities, net	101.8	145.2
Other [Member] | IPL [Member]
Deferred tax assets, gross	(64.0)	(70.4)
Deferred tax liabilities, gross	103.2	147.5
Deferred tax assets and liabilities, net	39.2	77.1
Other [Member] | WPL [Member]
Deferred tax assets, gross	(37.6)	(41.2)
Deferred tax liabilities, gross	75.6	83.7
Deferred tax assets and liabilities, net	38.0	42.5
Subtotal [Member]
Deferred tax assets, gross	(671.7)	(744.9)
Deferred tax liabilities, gross	2,647.7	2,507.0
Deferred tax assets and liabilities, net	$ 1,976.0	$ 1,762.1