Summary Of Significant Accounting Policies (Schedule Of Average Rates Of Depreciation) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Electric - generation [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	3.50%	3.50%	3.60%
Electric - generation [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	3.50%	3.10%	3.20%
Electric - distribution [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	2.40%	2.40%	2.40%
Electric - distribution [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	2.60%	2.60%	2.70%
Electric - other [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	4.50%	4.20%	4.00%
Electric - other [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	6.90%	4.70%	4.50%
Gas [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	3.40%	3.30%	3.20%
Gas [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	2.50%	2.50%	2.50%
Other [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	4.00%	3.90%	3.90%
Other [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	6.00%	5.90%	6.00%