Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Operating revenues	$ 843.8	$ 897.4
Operating income (loss)	145.9	152.9
Income (loss) from continuing operations, net of tax	97.6	96.6
Loss from discontinued operations, net of tax	(1.1)	0.0
Net income (loss) attributable to common shareowners	96.5	96.6
IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	458.7	489.0
Operating income (loss)	62.0	65.5
Net income (loss) attributable to common shareowners	45.6	47.5
WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	375.6	397.1
Operating income (loss)	78.8	80.8
Net income (loss) attributable to common shareowners	46.5	44.9
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	668.9	671.3
Operating income (loss)	109.8	104.7
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	361.6	362.6
Operating income (loss)	43.4	40.3
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	307.3	308.7
Operating income (loss)	66.4	64.4
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	152.2	198.4
Operating income (loss)	28.8	36.3
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	84.2	111.2
Operating income (loss)	15.8	20.6
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	68.0	87.2
Operating income (loss)	13.0	15.7
Other Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	13.2	16.4
Operating income (loss)	2.2	5.3
Other Utilities [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	12.9	15.2
Operating income (loss)	2.8	4.6
Other Utilities [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	0.3	1.2
Operating income (loss)	(0.6)	0.7
Utilities Business [Member]
Segment Reporting Information [Line Items]
Operating revenues	834.3	886.1
Operating income (loss)	140.8	146.3
Income (loss) from continuing operations, net of tax	92.1
Loss from discontinued operations, net of tax	0.0
Net income (loss) attributable to common shareowners	92.1	92.4
Non-Regulated [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	9.5	11.3
Operating income (loss)	5.1	6.6
Income (loss) from continuing operations, net of tax	5.5
Loss from discontinued operations, net of tax	(1.1)
Net income (loss) attributable to common shareowners	$ 4.4	$ 4.2