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Income Taxes (Schedule Of Effective Income Tax Rates) (Details) | 12 Months Ended
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Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Effective Tax Rate [Line Items] |  |  |
Statutory federal income tax rate | 35.00% | 35.00% | 35.00%
State income taxes, net of federal benefits | 5.40% | 5.20% | 5.40%
Effect of rate-making on property-related differences | (8.50%) | (6.80%) | (7.50%)
Production tax credits | (7.20%) | (7.20%) | (7.10%)
Adjustment of prior period taxes | (0.80%) | 0.80% | (1.30%)
Other items, net | (0.50%) | (1.10%) | (1.50%)
Overall income tax rate | 13.40% | 15.30% | 10.10%
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 | 6.40% | 6.20% | 6.10%
Effect of rate-making on property-related differences | (16.20%) | (17.20%) | (21.90%)
Production tax credits | (6.30%) | (8.30%) | (9.60%)
Adjustment of prior period taxes | (1.20%) | 0.70% | (3.00%)
Other items, net | (0.30%) | (1.20%) | (1.20%)
Overall income tax rate | (2.70%) | (13.10%) | (34.20%)
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 | (0.70%) | (0.50%) | (0.70%)
Production tax credits | (6.20%) | (7.10%) | (6.60%)
Adjustment of prior period taxes | (0.10%) | 0.10% | 0.00%
Other items, net | (0.50%) | (0.80%) | (0.80%)
Overall income tax rate | 32.60% | 31.80% | 32.00%
IPL's tax benefit riders [Member] |  |  |
Effective Tax Rate [Line Items] |  |  |
IPL’s tax benefit riders | (10.00%) | (10.60%) | (12.90%)
IPL's tax benefit riders [Member] | IPL [Member] |  |  |
Effective Tax Rate [Line Items] |  |  |
IPL’s tax benefit riders | (20.10%) | (28.30%) | (39.60%)

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