Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%	35.00%
State income taxes, net of federal benefits	5.70%	4.60%	4.80%
Production tax credits	(5.80%)	(6.60%)	(2.40%)
Effect of rate-making on property-related differences	(5.00%)	(2.00%)	(4.20%)
Adjustment of prior period taxes	0.00%	0.20%	0.30%
Federal Health Care Legislation	0.00%	0.00%	1.60%
Other items, net	(1.40%)	(0.90%)	(2.80%)
Overall income tax rate	20.80%	16.90%	32.30%
IPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%	35.00%
State income taxes, net of federal benefits	5.80%	4.30%	4.10%
Production tax credits	(9.60%)	(9.10%)	(4.10%)
Effect of rate-making on property-related differences	(14.20%)	(5.30%)	(8.90%)
Adjustment of prior period taxes	0.20%	1.70%	(1.80%)
Federal Health Care Legislation	0.00%	0.00%	2.00%
Other items, net	(1.60%)	(2.80%)	(3.50%)
Overall income tax rate	(15.20%)	(2.70%)	22.80%
WPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	35.00%	35.00%	35.00%
State income taxes, net of federal benefits	5.50%	5.00%	5.10%
Production tax credits	(4.70%)	(6.00%)	(1.40%)
Effect of rate-making on property-related differences	(1.10%)	(0.50%)	(1.10%)
Adjustment of prior period taxes	(0.30%)	0.00%	2.00%
Federal Health Care Legislation	0.00%	0.00%	1.20%
Other items, net	(0.80%)	(0.10%)	(1.60%)
Overall income tax rate	36.30%	33.40%	39.20%
State Apportionment [Member]
Effective Tax Rate [Line Items]
State apportionment change due to announced sale of RMT	3.50%	0.00%	0.00%
State Apportionment [Member] \| IPL [Member]
Effective Tax Rate [Line Items]
State apportionment change due to announced sale of RMT	6.20%	0.00%	0.00%
State Apportionment [Member] \| WPL [Member]
Effective Tax Rate [Line Items]
State apportionment change due to announced sale of RMT	2.70%	0.00%	0.00%
Tax Benefit Rider [Member]
Effective Tax Rate [Line Items]
IPL’s electric tax benefit rider	(11.20%)	(8.80%)	0.00%
Tax Benefit Rider [Member] \| IPL [Member]
Effective Tax Rate [Line Items]
IPL’s electric tax benefit rider	(37.00%)	(26.50%)	0.00%
Wisconsin Tax Legislation [Member]
Effective Tax Rate [Line Items]
Wisconsin tax legislation	0.00%	(4.60%)	0.00%

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Effective income tax rate reconciliation tax benefit rider

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Effective income tax rate reconciliation tax legislation

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A ratio calculated by dividing the reported amount of income tax expense attributable to continuing operations for the period by GAAP-basis pretax income from continuing operations.

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The domestic federal statutory tax rate applicable under enacted tax laws to the Company's pretax income from continuing operations for the period. The "statutory" tax rate is the regular tax rate if there are alternative tax systems.

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The portion of the difference between total income tax expense or benefit as reported in the Income Statement and the expected income tax expense or benefit that is attributable to changes in the income tax laws or rates.

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Percentage of difference between the effective income tax rate and domestic federal statutory income tax rate attributable to the deduction received under enacted tax laws for Medicare prescription drug benefits (subsidies).

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to the deduction for qualified production activities received under enacted tax laws.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to all other items not otherwise listed in the existing taxonomy.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to revisions in previously reported amounts of income tax provision.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by the state and local income tax expense or benefit, net of the federal tax benefit (expense) thereon, recorded during the period.

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