Benefit Plans (Amounts Recognized On The Consolidated Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations	$ (509.1)	$ (504.0)
Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	0.0	0.0
Current liabilities	(2.3)	(2.2)
Pension and other benefit obligations	(364.1)	(350.2)
Net amounts recognized at December 31	(366.4)	(352.4)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	505.2	509.1
Prior service credit	(5.8)	(6.5)
Net amount recognized at December 31	499.4	502.6
Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	7.5	8.8
Current liabilities	(9.6)	(9.1)
Pension and other benefit obligations	(104.9)	(110.9)
Net amounts recognized at December 31	(107.0)	(111.2)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	44.5	47.4
Prior service credit	(1.1)	(1.3)
Net amount recognized at December 31	43.4	46.1
IPL [Member]
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations	(178.4)	(173.8)
IPL [Member] | Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	0.0	0.0
Current liabilities	(0.6)	(0.5)
Pension and other benefit obligations	(155.5)	(148.7)
Net amounts recognized at December 31	(156.1)	(149.2)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	218.8	218.9
Prior service credit	(1.8)	(2.1)
Net amount recognized at December 31	217.0	216.8
IPL [Member] | Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	4.7	5.9
Current liabilities	(1.9)	(2.0)
Pension and other benefit obligations	(18.6)	(20.4)
Net amounts recognized at December 31	(15.8)	(16.5)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	18.8	18.7
Prior service credit	0.0	0.0
Net amount recognized at December 31	18.8	18.7
WPL [Member]
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations	(217.7)	(213.7)
WPL [Member] | Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	0.0	0.0
Current liabilities	(0.1)	(0.1)
Pension and other benefit obligations	(154.3)	(144.7)
Net amounts recognized at December 31	(154.4)	(144.8)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	223.0	224.7
Prior service credit	(1.3)	(1.5)
Net amount recognized at December 31	221.7	223.2
WPL [Member] | Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	2.8	2.9
Current liabilities	(7.4)	(6.8)
Pension and other benefit obligations	(61.9)	(67.8)
Net amounts recognized at December 31	(66.5)	(71.7)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	19.9	23.6
Prior service credit	(1.1)	(1.3)
Net amount recognized at December 31	$ 18.8	$ 22.3