Summary Of Significant Accounting Policies (Schedule Of Allowance For Funds Used During Construction Recovery Rate) (Details) - MW		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
IPL [Member] | IPL (Marshalltown CWIP) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates	[1]	7.80%	7.90%	7.90%
IPL [Member] | IPL (Wind generation CWIP) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates	[2]	7.60%
IPL [Member] | IPL (other CWIP) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates		7.60%	7.70%	7.70%
IPL [Member] | Marshalltown Generating Station [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Return on common equity for calculation of AFUDC		10.30%
IPL [Member] | Expansion of Wind Generation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Return on common equity for calculation of AFUDC		10.00%
Electric capacity of wind farm (in megawatts)		500
WPL [Member] | WPL (retail jurisdiction) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates		7.60%	8.20%	8.20%
WPL [Member] | WPL (wholesale jurisdiction) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates		6.00%	6.70%	7.90%
WPL [Member] | Expansion of Wind Generation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Electric capacity of wind farm (in megawatts)		129

[1] In 2013, the IUB issued an order establishing rate-making principles that require a 10.3% return on common equity for the calculation of AFUDC related to the construction of Marshalltown.

[2] In 2016, the IUB issued an order establishing rate-making principles that require a return on common equity for the calculation of AFUDC related to the construction of up to 500 MW of new wind generation equal to the greater of 10.0% or whatever percentage the IUB finds reasonable during IPL’s most recent retail electric rate proceeding.