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%