Summary Of Significant Accounting Policies (Schedule Of Allowance For Funds Used During Construction Recovery Rate) (Details)		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
IPL [Member] | IPL (Marshalltown CWIP) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates	[1]	7.90%	7.90%	8.00%
IPL [Member] | IPL (other CWIP) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates		7.70%	7.70%	7.80%
IPL [Member] | Marshalltown Generating Station [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Return on common equity for calculation of AFUDC		10.30%
WPL [Member] | WPL (retail jurisdiction) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates		8.20%	8.20%	8.20%
WPL [Member] | WPL (wholesale jurisdiction) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates		6.70%	7.90%	4.10%

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