Benefit Plans (Estimated Amoritization From Regulatory Assets, Regulatory Liabilities And Accumulated Other Comprehensive Loss) (Details) - Scenario, Forecast [Member] $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	$ 35.2
Prior service credit	(0.7)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	34.5
Defined Benefit Pension Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	15.0
Prior service credit	(0.2)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	14.8
Defined Benefit Pension Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	17.2
Prior service credit	(0.2)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	17.0
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	3.4
Prior service credit	(0.2)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	3.2
Other Postretirement Benefits Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	1.2
Prior service credit	0.0
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	1.2
Other Postretirement Benefits Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	2.0
Prior service credit	(0.2)
Estimated amortization from regulatory assets, regulatory liabilities and AOCL	$ 1.8