Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Operating revenues	$ 898.9	$ 843.1	$ 2,513.5	$ 2,546.2
Operating income (loss)	235.9	194.8	497.8	452.3
Income (loss) from continuing operations, net of tax	180.0	155.2	345.5	325.3
Loss from discontinued operations, net of tax	(0.1)	(1.9)	(1.4)	(2.2)
Net income (loss) attributable to common shareowners	179.9	153.3	344.1	323.1
IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	504.6	476.2	1,375.8	1,417.0
Operating income (loss)	117.0	93.9	216.3	185.4
Net income (loss) attributable to common shareowners	117.4	102.5	181.9	164.3
WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	382.6	354.4	1,104.4	1,089.3
Operating income (loss)	110.3	93.9	259.4	241.6
Net income (loss) attributable to common shareowners	67.5	61.6	151.1	151.0
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	835.8	771.2	2,147.5	2,090.9
Operating income (loss)	232.8	190.8	438.4	374.2
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	468.6	435.9	1,170.6	1,164.7
Operating income (loss)	119.4	94.7	193.6	150.2
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	367.2	335.3	976.9	926.2
Operating income (loss)	113.4	96.1	244.8	224.0
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	38.0	47.2	288.1	364.8
Operating income (loss)	(5.7)	(4.4)	28.6	41.3
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	23.1	28.7	164.1	208.1
Operating income (loss)	(2.9)	(2.8)	15.3	22.1
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	14.9	18.5	124.0	156.7
Operating income (loss)	(2.8)	(1.6)	13.3	19.2
Other Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	13.4	12.2	44.6	50.6
Operating income (loss)	0.2	1.4	8.7	11.5
Other Utilities [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	12.9	11.6	41.1	44.2
Operating income (loss)	0.5	2.0	7.4	13.1
Other Utilities [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	0.5	0.6	3.5	6.4
Operating income (loss)	(0.3)	(0.6)	1.3	(1.6)
Utilities Business [Member]
Segment Reporting Information [Line Items]
Operating revenues	887.2	830.6	2,480.2	2,506.3
Operating income (loss)	227.3	187.8	475.7	427.0
Income (loss) from continuing operations, net of tax	184.9	164.1	333.0	315.3
Loss from discontinued operations, net of tax	0.0	0.0	0.0	0.0
Net income (loss) attributable to common shareowners	184.9	164.1	333.0	315.3
Non-Regulated [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	11.7	12.5	33.3	39.9
Operating income (loss)	8.6	7.0	22.1	25.3
Income (loss) from continuing operations, net of tax	(4.9)	(8.9)	12.5	10.0
Loss from discontinued operations, net of tax	(0.1)	(1.9)	(1.4)	(2.2)
Net income (loss) attributable to common shareowners	$ (5.0)	$ (10.8)	$ 11.1	$ 7.8