v2.4.0.6

Summary Of Significant Accounting Policies (Schedule Of Average Rates Of Depreciation) (Details) | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Electric - generation [Member] | IPL [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average rate of depreciation | 3.70% | 3.50% | 3.70%
Electric - generation [Member] | WPL [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average rate of depreciation | 3.20% | 3.30% | 2.90%
Electric - distribution [Member] | IPL [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average rate of depreciation | 2.50% | 2.40% | 2.70%
Electric - distribution [Member] | WPL [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average rate of depreciation | 2.90% | 2.90% | 2.60%
Gas [Member] | IPL [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average rate of depreciation | 3.40% | 3.50% | 3.30%
Gas [Member] | WPL [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average rate of depreciation | 2.60% | 2.60% | 2.20%
Other [Member] | IPL [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average rate of depreciation | 4.50% | 4.80% | 4.90%
Other [Member] | WPL [Member] |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |
Average rate of depreciation | 5.30% | 5.20% | 6.50%

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- Definition Composite depreciation rate for public utility plants in service. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration