Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax [Line Items]
Statutory federal income tax rate		35.00%	35.00%	35.00%
Other assets, deferred charges and other		$ 41.0
Scenario, Forecast [Member]
Income Tax [Line Items]
Deductions in income tax return	$ 670.0
IPL [Member]
Income Tax [Line Items]
Statutory federal income tax rate		35.00%	35.00%	35.00%
Other assets, deferred charges and other		$ 0.0
IPL [Member] | Scenario, Forecast [Member]
Income Tax [Line Items]
Deductions in income tax return	500.0
WPL [Member]
Income Tax [Line Items]
Statutory federal income tax rate		35.00%	35.00%	35.00%
Other assets, deferred charges and other		$ 0.0
WPL [Member] | Scenario, Forecast [Member]
Income Tax [Line Items]
Deductions in income tax return	$ 140.0
Subsequent Event [Member]
Income Tax [Line Items]
Statutory federal income tax rate	21.00%
Subsequent Event [Member] | IPL [Member]
Income Tax [Line Items]
Statutory federal income tax rate	21.00%
Subsequent Event [Member] | WPL [Member]
Income Tax [Line Items]
Statutory federal income tax rate	21.00%