Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Revenues	$ 915.7	$ 987.2
Operating income (loss)	188.3	176.8
Net income (loss) attributable to common shareowners	170.0	125.1
Net income	172.6	127.7
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	518.9	555.1
Operating income (loss)	96.7	73.5
Net income (loss) attributable to common shareowners	82.6	53.3
Net income	85.2	55.9
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	375.2	415.2
Operating income (loss)	93.8	98.1
Net income	89.6	65.7
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	730.3	743.4
Operating income (loss)	146.2	126.4
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	424.8	419.8
Operating income (loss)	67.0	46.8
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	305.5	323.6
Operating income (loss)	79.2	79.6
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	152.2	215.8
Operating income (loss)	41.6	45.2
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	83.0	124.6
Operating income (loss)	27.3	26.3
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	69.2	91.2
Operating income (loss)	14.3	18.9
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	11.6	11.1
Operating income (loss)	2.7	0.0
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	11.1	10.7
Operating income (loss)	2.4	0.4
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	0.5	0.4
Operating income (loss)	0.3	(0.4)
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	894.1	970.3
Operating income (loss)	190.5	171.6
Net income (loss) attributable to common shareowners	172.2	119.0
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member]
Segment Reporting Information [Line Items]
Revenues	21.6	16.9
Operating income (loss)	(2.2)	5.2
Net income (loss) attributable to common shareowners	$ (2.2)	$ 6.1