Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Revenues	$ 763.1	$ 790.2	$ 1,678.8	$ 1,777.4
Operating income (loss)	168.1	149.8	356.4	326.6
Net income attributable to common shareowners	134.4	94.6	304.4	219.7
Net income	136.9	97.1	309.5	224.8
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	431.9	441.2	950.8	996.3
Operating income (loss)	88.7	74.5	185.4	148.0
Net income attributable to common shareowners	59.8	45.0	142.4	98.3
Net income	62.3	47.5	147.5	103.4
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	312.3	326.1	687.5	741.3
Operating income (loss)	71.7	67.0	165.5	165.1
Net income	57.6	42.0	147.2	107.7
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	675.2	691.2	1,405.5	1,434.6
Operating income (loss)	152.1	132.9	298.3	259.3
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	388.4	392.3	813.2	812.1
Operating income (loss)	82.1	68.9	149.1	115.7
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	286.8	298.9	592.3	622.5
Operating income (loss)	70.0	64.0	149.2	143.6
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	58.9	65.2	211.1	281.0
Operating income (loss)	7.1	7.2	48.7	52.4
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	33.9	38.4	116.9	163.0
Operating income (loss)	5.2	4.2	32.5	30.5
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	25.0	26.8	94.2	118.0
Operating income (loss)	1.9	3.0	16.2	21.9
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	10.1	10.9	21.7	22.0
Operating income (loss)	1.2	1.4	3.9	1.4
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	9.6	10.5	20.7	21.2
Operating income (loss)	1.4	1.4	3.8	1.8
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	0.5	0.4	1.0	0.8
Operating income (loss)	(0.2)	0.0	0.1	(0.4)
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	744.2	767.3	1,638.3	1,737.6
Operating income (loss)	160.4	141.5	350.9	313.1
Net income attributable to common shareowners	117.4	87.0	289.6	206.0
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member]
Segment Reporting Information [Line Items]
Revenues	18.9	22.9	40.5	39.8
Operating income (loss)	7.7	8.3	5.5	13.5
Net income attributable to common shareowners	$ 17.0	$ 7.6	$ 14.8	$ 13.7