Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Revenues	$ 987.2	$ 916.3
Operating income (loss)	176.8	165.7
Net income attributable to common shareowners	125.1	120.9
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	555.1	525.8
Operating income (loss)	73.5	75.6
Net income attributable to common shareowners	53.3	46.7
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	415.2	381.7
Operating income (loss)	98.1	84.0
Net income attributable to common shareowners	65.7	54.0
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	743.4	708.7
Operating income (loss)	126.4	126.7
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	419.8	405.7
Operating income (loss)	46.8	57.5
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	323.6	303.0
Operating income (loss)	79.6	69.2
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	215.8	185.6
Operating income (loss)	45.2	31.5
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	124.6	108.1
Operating income (loss)	26.3	16.9
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	91.2	77.5
Operating income (loss)	18.9	14.6
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	11.1	13.2
Operating income (loss)	0.0	1.4
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	10.7	12.0
Operating income (loss)	0.4	1.2
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	0.4	1.2
Operating income (loss)	(0.4)	0.2
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	970.3	907.5
Operating income (loss)	171.6	159.6
Net income attributable to common shareowners	119.0	100.7
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member]
Segment Reporting Information [Line Items]
Revenues	16.9	8.8
Operating income (loss)	5.2	6.1
Net income attributable to common shareowners	$ 6.1	$ 20.2