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Summary Of Significant Accounting Policies (Narrative) (Details) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 USD ($) customer MW | Dec. 31, 2016 | Dec. 31, 2015
Adjustments for New Accounting Principle, Early Adoption [Member] |  |  |  |
New Accounting Standards: |  |  |  |
Decrease to deferred tax liabilities due to adoption of new accounting standard | $ |  | $ (3.1) |  |
Increase to retained earnings due to adoption of new accounting standard | $ |  | $ 3.1 |  |
IPL [Member] |  |  |  |
General: |  |  |  |
Generation and distribution of steam, number of customers served (in customers) | customer |  | 2 |  |
Property, Plant and Equipment: |  |  |  |
AFUDC accrual recorded, percentage of estimated CWIP |  | 100.00% |  |
Operating Revenues: |  |  |  |
Estimated recovery of overaccrued operating revenue, reflected on customer billing, maximum period |  | 2 years |  |
WPL [Member] |  |  |  |
Property, Plant and Equipment: |  |  |  |
AFUDC accrual recorded, percentage of estimated CWIP |  | 50.00% |  |
AFUDC rates, projects with approval |  | 100.00% |  |
Operating Revenues: |  |  |  |
Final settlement recovery of overaccrued operating revenue, reflected on customer billing, maximum period |  | 2 years |  |
Alliant Energy Finance, LLC [Member] |  |  |  |
General: |  |  |  |
Ownership interest |  | 50.00% |  |
Electric capacity of wind farm (in megawatts) | MW |  | 225 |  |
Sheboygan Falls Energy Facility [Member] |  |  |  |
General: |  |  |  |
Fossil-fueled EGU capacity (in megawatts) | MW |  | 347 |  |
Capital lease, lease term |  | 20 years |  |
Electric - generation [Member] | IPL [Member] |  |  |  |
Property, Plant and Equipment: |  |  |  |
Average rate of depreciation |  | 3.50% | 3.50% | 3.60%
Electric - generation [Member] | WPL [Member] |  |  |  |
Property, Plant and Equipment: |  |  |  |
Average rate of depreciation |  | 3.50% | 3.10% | 3.20%
Electric - distribution [Member] | IPL [Member] |  |  |  |
Property, Plant and Equipment: |  |  |  |
Average rate of depreciation |  | 2.40% | 2.40% | 2.40%
Electric - distribution [Member] | WPL [Member] |  |  |  |
Property, Plant and Equipment: |  |  |  |
Average rate of depreciation |  | 2.60% | 2.60% | 2.70%
Scenario, Forecast [Member] | Electric - generation [Member] | IPL [Member] |  |  |  |
Property, Plant and Equipment: |  |  |  |
Average rate of depreciation | 3.80% |  |  |
Scenario, Forecast [Member] | Electric - distribution [Member] | IPL [Member] |  |  |  |
Property, Plant and Equipment: |  |  |  |
Average rate of depreciation | 2.80% |  |  |

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