Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Operating revenues	$ 754.6	$ 717.2	$ 1,598.4	$ 1,614.6
Operating income (loss)	128.6	109.0	274.5	261.9
Income from continuing operations, net of tax	84.4	68.9	182.0	165.5
Loss from discontinued operations, net of tax	(0.5)	(1.3)	(1.6)	(1.3)
Net income (loss) attributable to common shareowners	83.9	67.6	180.4	164.2
IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	411.0	382.2	869.7	871.2
Operating income (loss)	48.0	33.8	110.0	99.3
Net income (loss) attributable to common shareowners	31.9	16.5	77.5	64.0
WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	334.3	324.7	709.9	721.8
Operating income (loss)	75.0	68.3	153.8	149.1
Net income (loss) attributable to common shareowners	43.2	39.2	89.7	84.1
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	675.9	640.4	1,344.8	1,311.7
Operating income (loss)	119.3	100.9	229.1	205.6
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	364.4	339.4	726.0	702.0
Operating income (loss)	44.5	33.9	87.9	74.2
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	311.5	301.0	618.8	609.7
Operating income (loss)	74.8	67.0	141.2	131.4
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	57.0	51.7	209.2	250.1
Operating income (loss)	1.9	(2.0)	30.7	34.3
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	34.5	29.8	118.7	141.0
Operating income (loss)	0.9	(2.4)	16.7	18.2
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	22.5	21.9	90.5	109.1
Operating income (loss)	1.0	0.4	14.0	16.1
Other Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	12.4	14.8	25.6	31.2
Operating income (loss)	1.8	3.2	4.0	8.5
Other Utilities [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	12.1	13.0	25.0	28.2
Operating income (loss)	2.6	2.3	5.4	6.9
Other Utilities [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	0.3	1.8	0.6	3.0
Operating income (loss)	(0.8)	0.9	(1.4)	1.6
Utilities Business [Member]
Segment Reporting Information [Line Items]
Operating revenues	745.3	706.9	1,579.6	1,593.0
Operating income (loss)	123.0	102.1	263.8	248.4
Income from continuing operations, net of tax	75.1	55.7	167.2	148.1
Loss from discontinued operations, net of tax	0.0	0.0	0.0	0.0
Net income (loss) attributable to common shareowners	75.1	55.7	167.2	148.1
Non-Regulated [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	9.3	10.3	18.8	21.6
Operating income (loss)	5.6	6.9	10.7	13.5
Income from continuing operations, net of tax	9.3	13.2	14.8	17.4
Loss from discontinued operations, net of tax	(0.5)	(1.3)	(1.6)	(1.3)
Net income (loss) attributable to common shareowners	$ 8.8	$ 11.9	$ 13.2	$ 16.1