Summary Of Significant Accounting Policies (Narrative) (Details) $ in Millions		12 Months Ended
	Apr. 20, 2016	Dec. 31, 2017	Dec. 31, 2016 USD ($) customer MW	Dec. 31, 2015	Dec. 31, 2014
General:
Common stock split conversion ratio (2:1)	2
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
Sheboygan Falls Energy Facility [Member]
General:
Fossil-fueled EGU capacity (in megawatts) | MW			347
Capital lease, lease term			20 years
Franklin County Wind Farm [Member]
General:
Wind EGU capacity (in megawatts) | MW			99
Electric Generation Equipment [Member] | IPL [Member]
Property, Plant and Equipment:
Average rate of depreciation			3.50%	3.60%	3.60%
Electric Generation Equipment [Member] | WPL [Member]
Property, Plant and Equipment:
Average rate of depreciation			3.10%	3.20%	3.20%
Electric - distribution [Member] | IPL [Member]
Property, Plant and Equipment:
Average rate of depreciation			2.40%	2.40%	2.50%
Electric - distribution [Member] | WPL [Member]
Property, Plant and Equipment:
Average rate of depreciation			2.60%	2.70%	2.70%
Gas [Member] | IPL [Member]
Property, Plant and Equipment:
Average rate of depreciation			3.30%	3.20%	3.30%
Gas [Member] | WPL [Member]
Property, Plant and Equipment:
Average rate of depreciation			2.50%	2.50%	2.50%
Scenario, Forecast [Member] | Electric Generation Equipment [Member] | WPL [Member]
Property, Plant and Equipment:
Average rate of depreciation		3.20%
Scenario, Forecast [Member] | Electric - distribution [Member] | WPL [Member]
Property, Plant and Equipment:
Average rate of depreciation		2.60%
Scenario, Forecast [Member] | Gas [Member] | WPL [Member]
Property, Plant and Equipment:
Average rate of depreciation		2.30%