Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Current deferred tax assets	$ (150.1)us-gaap_DeferredTaxAssetsNetCurrent	$ (136.7)us-gaap_DeferredTaxAssetsNetCurrent
Non-current deferred tax liabilities	2,321.1	2,112.7
Deferred tax liabilities, net of deferred tax assets	2,171.0us-gaap_DeferredTaxLiabilities	1,976.0us-gaap_DeferredTaxLiabilities
IPL [Member]
Deferred tax assets, gross	(376.4)	(336.0)
Deferred tax liabilities, gross	1,612.9	1,441.3
Deferred tax assets and liabilities, net	1,236.5	1,105.3
Current deferred tax assets	(104.9)	(87.7)
Non-current deferred tax liabilities	1,341.4	1,193.0
Deferred tax liabilities, net of deferred tax assets	1,236.5	1,105.3
WPL [Member]
Deferred tax assets, gross	(244.4)	(201.6)
Deferred tax liabilities, gross	1,176.9	1,055.4
Deferred tax assets and liabilities, net	932.5	853.8
Current deferred tax assets	(37.5)	(43.3)
Non-current deferred tax liabilities	970.0	897.1
Deferred tax liabilities, net of deferred tax assets	932.5	853.8
Property [Member]
Deferred tax assets, gross	0	0
Deferred tax liabilities, gross	2,627.8	2,316.3
Deferred tax assets and liabilities, net	2,627.8	2,316.3
Property [Member] \| IPL [Member]
Deferred tax assets, gross	0	0
Deferred tax liabilities, gross	1,531.0	1,338.1
Deferred tax assets and liabilities, net	1,531.0	1,338.1
Property [Member] \| WPL [Member]
Deferred tax assets, gross	0	0
Deferred tax liabilities, gross	964.4	859.1
Deferred tax assets and liabilities, net	964.4	859.1
Investment In ATC [Member]
Deferred tax assets, gross	0	0
Deferred tax liabilities, gross	131.6	120.7
Deferred tax assets and liabilities, net	131.6	120.7
Investment In ATC [Member] \| WPL [Member]
Deferred tax assets, gross	0	0
Deferred tax liabilities, gross	131.6	120.7
Deferred tax assets and liabilities, net	131.6	120.7
Net operating losses carryforward - state [Member]
Deferred tax assets, gross	(45.7)	(35.3)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(45.7)	(35.3)
Regulatory liability - IPL's tax benefit riders [Member]
Deferred tax assets, gross	(100.9)	(107.8)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(100.9)	(107.8)
Regulatory liability - IPL's tax benefit riders [Member] \| IPL [Member]
Deferred tax assets, gross	(100.9)	(107.8)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(100.9)	(107.8)
Federal credit carryforward [Member]
Deferred tax assets, gross	(201.0)	(167.8)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(201.0)	(167.8)
Federal credit carryforward [Member] \| IPL [Member]
Deferred tax assets, gross	(67.7)	(52.9)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(67.7)	(52.9)
Federal credit carryforward [Member] \| WPL [Member]
Deferred tax assets, gross	(75.2)	(57.1)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(75.2)	(57.1)
Net operating losses carryforward - federal [Member]
Deferred tax assets, gross	(332.8)	(251.9)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(332.8)	(251.9)
Net operating losses carryforward - federal [Member] \| IPL [Member]
Deferred tax assets, gross	(160.6)	(111.3)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(160.6)	(111.3)
Net operating losses carryforward - federal [Member] \| WPL [Member]
Deferred tax assets, gross	(128.9)	(106.9)
Deferred tax liabilities, gross	0	0
Deferred tax assets and liabilities, net	(128.9)	(106.9)
Other [Member]
Deferred tax assets, gross	(88.1)	(108.9)
Deferred tax liabilities, gross	180.1	210.7
Deferred tax assets and liabilities, net	92.0	101.8
Other [Member] \| IPL [Member]
Deferred tax assets, gross	(47.2)	(64.0)
Deferred tax liabilities, gross	81.9	103.2
Deferred tax assets and liabilities, net	34.7	39.2
Other [Member] \| WPL [Member]
Deferred tax assets, gross	(40.3)	(37.6)
Deferred tax liabilities, gross	80.9	75.6
Deferred tax assets and liabilities, net	40.6	38.0
Subtotal [Member]
Deferred tax assets, gross	(768.5)	(671.7)
Deferred tax liabilities, gross	2,939.5	2,647.7
Deferred tax assets and liabilities, net	$ 2,171.0	$ 1,976.0

Total deferred tax (assets) and liabilities, Gross

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Amount of deferred tax liability attributable to taxable temporary differences.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards expected to be realized or consumed within one year or operating cycle, if longer.

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Amount of deferred tax liability attributable to taxable temporary differences net of deferred tax asset attributable to deductible temporary differences and carryforwards after valuation allowances.

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