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Income Taxes (Schedule Of Effective Income Tax Rates) (Details) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Effective Tax Rate [Line Items] |  |  |
Statutory federal income tax rate | 21.00% | 21.00% | 21.00%
State income taxes, net of federal benefits | 2.00% | 7.00% | 7.00%
Production tax credits | (17.00%) | (9.00%) | (5.00%)
Amortization of excess deferred taxes | (13.00%) | (1.00%) | (1.00%)
Effect of rate-making on property-related differences | (3.00%) | (6.00%) | (8.00%)
Adjustment for prior period taxes | 1.00% | 1.00% | (2.00%)
Federal Tax Reform adjustments | 0.00% | 0.00% | (1.00%)
Other items, net | (1.00%) | (1.00%) | (1.00%)
Overall income tax rate | (10.00%) | 11.00% | 8.00%
IPL [Member] |  |  |
Effective Tax Rate [Line Items] |  |  |
Statutory federal income tax rate | 21.00% | 21.00% | 21.00%
State income taxes, net of federal benefits | (1.00%) | 8.00% | 8.00%
Production tax credits | (28.00%) | (13.00%) | (5.00%)
Amortization of excess deferred taxes | (5.00%) | 0.00% | 0.00%
Effect of rate-making on property-related differences | (4.00%) | (10.00%) | (14.00%)
Adjustment for prior period taxes | 1.00% | 3.00% | (5.00%)
Federal Tax Reform adjustments | 0.00% | 0.00% | 0.00%
Other items, net | 0.00% | 0.00% | (1.00%)
Overall income tax rate | (16.00%) | 8.00% | (1.00%)
WPL [Member] |  |  |
Effective Tax Rate [Line Items] |  |  |
Statutory federal income tax rate | 21.00% | 21.00% | 21.00%
State income taxes, net of federal benefits | 6.00% | 6.00% | 6.00%
Production tax credits | (7.00%) | (5.00%) | (7.00%)
Amortization of excess deferred taxes | (26.00%) | (2.00%) | 0.00%
Effect of rate-making on property-related differences | (2.00%) | (3.00%) | (2.00%)
Adjustment for prior period taxes | 0.00% | 0.00% | 0.00%
Federal Tax Reform adjustments | 0.00% | 0.00% | (2.00%)
Other items, net | 0.00% | 0.00% | (1.00%)
Overall income tax rate | (8.00%) | 17.00% | 15.00%
IPL's tax benefit riders [Member] |  |  |
Effective Tax Rate [Line Items] |  |  |
IPL’s tax benefit riders | 0.00% | (1.00%) | (2.00%)
IPL's tax benefit riders [Member] | IPL [Member] |  |  |
Effective Tax Rate [Line Items] |  |  |
IPL’s tax benefit riders | 0.00% | (1.00%) | (5.00%)

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