Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenues	$ 990.2	$ 928.6	$ 2,767.6	$ 2,661.0
Operating income (loss)	290.2	256.1	616.8	573.0
Net income attributable to common shareowners	226.0	205.5	445.7	426.8
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	596.5	547.6	1,592.8	1,548.2
Operating income (loss)	173.5	143.1	321.5	296.4
Net income attributable to common shareowners	141.1	126.5	239.4	224.9
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	372.1	370.7	1,113.4	1,083.2
Operating income (loss)	108.3	104.2	273.4	251.6
Net income attributable to common shareowners	75.5	76.3	183.2	170.1
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	915.9	861.2	2,350.5	2,296.2
Operating income (loss)	283.7	248.7	543.0	510.2
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	560.9	509.2	1,373.0	1,337.0
Operating income (loss)	175.1	144.7	290.8	275.7
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	355.0	352.0	977.5	959.2
Operating income (loss)	108.6	104.0	252.2	234.5
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	41.5	44.8	322.5	299.0
Operating income (loss)	(4.7)	(2.0)	47.7	34.9
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	24.8	26.7	187.8	177.0
Operating income (loss)	(4.2)	(3.1)	26.3	16.3
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	16.7	18.1	134.7	122.0
Operating income (loss)	(0.5)	1.1	21.4	18.6
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	11.2	12.3	33.2	36.2
Operating income (loss)	2.8	0.6	4.2	2.9
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	10.8	11.7	32.0	34.2
Operating income (loss)	2.6	1.5	4.4	4.4
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	0.4	0.6	1.2	2.0
Operating income (loss)	0.2	(0.9)	(0.2)	(1.5)
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	968.6	918.3	2,706.2	2,631.4
Operating income (loss)	281.8	247.3	594.9	548.0
Net income attributable to common shareowners	216.6	202.8	422.6	395.0
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member]
Segment Reporting Information [Line Items]
Revenues	21.6	10.3	61.4	29.6
Operating income (loss)	8.4	8.8	21.9	25.0
Net income attributable to common shareowners	$ 9.4	$ 2.7	$ 23.1	$ 31.8