Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Revenues	$ 790.2	$ 816.1	$ 1,777.4	$ 1,732.4
Operating income (loss)	149.8	151.2	326.6	316.9
Net income attributable to common shareowners	94.6	100.4	219.7	221.3
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	441.2	474.8	996.3	1,000.6
Operating income (loss)	74.5	77.7	148.0	153.3
Net income attributable to common shareowners	45.0	51.7	98.3	98.4
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	326.1	330.8	741.3	712.5
Operating income (loss)	67.0	63.4	165.1	147.4
Net income attributable to common shareowners	42.0	39.8	107.7	93.8
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	691.2	726.3	1,434.6	1,435.0
Operating income (loss)	132.9	134.8	259.3	261.5
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	392.3	422.1	812.1	827.8
Operating income (loss)	68.9	73.5	115.7	131.0
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	298.9	304.2	622.5	607.2
Operating income (loss)	64.0	61.3	143.6	130.5
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	65.2	68.6	281.0	254.2
Operating income (loss)	7.2	5.4	52.4	36.9
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	38.4	42.2	163.0	150.3
Operating income (loss)	4.2	2.5	30.5	19.4
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	26.8	26.4	118.0	103.9
Operating income (loss)	3.0	2.9	21.9	17.5
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	10.9	10.7	22.0	23.9
Operating income (loss)	1.4	0.9	1.4	2.3
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	10.5	10.5	21.2	22.5
Operating income (loss)	1.4	1.7	1.8	2.9
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	0.4	0.2	0.8	1.4
Operating income (loss)	0.0	(0.8)	(0.4)	(0.6)
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	767.3	805.6	1,737.6	1,713.1
Operating income (loss)	141.5	141.1	313.1	300.7
Net income attributable to common shareowners	87.0	91.5	206.0	192.2
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member]
Segment Reporting Information [Line Items]
Revenues	22.9	10.5	39.8	19.3
Operating income (loss)	8.3	10.1	13.5	16.2
Net income attributable to common shareowners	$ 7.6	$ 8.9	$ 13.7	$ 29.1