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Income Taxes (Schedule Of Effective Income Tax Rates) (Details) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
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% | 5.40% | 5.20%
Effect of rate-making on property-related differences | (8.50%) | (8.50%) | (6.80%)
Production tax credits | (6.10%) | (7.20%) | (7.20%)
Impact of Tax Reform | (3.40%) | (0.00%) | (0.00%)
Other items, net | (2.40%) | (1.30%) | (0.30%)
Overall income tax rate | 12.50% | 13.40% | 15.30%
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 | 6.50% | 6.40% | 6.20%
Effect of rate-making on property-related differences | (19.10%) | (16.20%) | (17.20%)
Production tax credits | (6.70%) | (6.30%) | (8.30%)
Impact of Tax Reform | 1.70% | (0.00%) | (0.00%)
Other items, net | (3.70%) | (1.50%) | (0.50%)
Overall income tax rate | (5.00%) | (2.70%) | (13.10%)
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 | 5.10% | 5.10% | 5.10%
Effect of rate-making on property-related differences | (1.70%) | (0.70%) | (0.50%)
Production tax credits | (7.10%) | (6.20%) | (7.10%)
Impact of Tax Reform | (5.80%) | (0.00%) | (0.00%)
Other items, net | (0.60%) | (0.60%) | (0.70%)
Overall income tax rate | 24.90% | 32.60% | 31.80%
IPL's tax benefit riders [Member] |  |  |
Effective Tax Rate [Line Items] |  |  |
IPL’s tax benefit riders | (7.60%) | (10.00%) | (10.60%)
IPL's tax benefit riders [Member] | IPL [Member] |  |  |
Effective Tax Rate [Line Items] |  |  |
IPL’s tax benefit riders | (18.70%) | (20.10%) | (28.30%)

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