Segments Of Business (Schedule Of Segments Of Business) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]
Operating revenues	$ 750.3	$ 718.0	$ 1,703.1	$ 1,577.6
Operating income (loss)	103.3	103.2	257.5	223.9
Income (loss) from continuing operations, net of tax	62.1	65.9	170.1	138.8
Income (loss) from discontinued operations, net of tax	(0.3)	(0.6)	(0.3)	(3.6)
Net income (loss) attributable to common shareowners	61.8	65.3	169.8	135.2
IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	411.9	383.4	940.8	861.3
Operating income (loss)	34.0	34.7	91.5	75.8
Net income (loss) attributable to common shareowners	18.4	22.2	61.8	45.1
WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	324.5	319.9	734.9	689.7
Operating income (loss)	60.0	59.7	147.7	132.4
Net income (loss) attributable to common shareowners	34.6	34.4	89.4	76.4
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	643.9	612.1	1,319.7	1,245.3
Operating income (loss)	89.1	85.9	183.4	159.5
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	354.6	329.6	728.8	679.8
Operating income (loss)	29.0	29.4	55.5	46.6
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	289.3	282.5	590.9	565.5
Operating income (loss)	60.1	56.5	127.9	112.9
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	76.9	73.4	317.6	270.7
Operating income (loss)	2.7	5.6	45.7	42.9
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	43.7	42.0	179.4	156.3
Operating income (loss)	1.6	2.6	24.9	23.3
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	33.2	31.4	138.2	114.4
Operating income (loss)	1.1	3.0	20.8	19.6
Other Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	15.6	17.8	38.4	35.0
Operating income (loss)	2.2	2.9	10.1	5.8
Other Utilities [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	13.6	11.8	32.6	25.2
Operating income (loss)	3.4	2.7	11.1	5.9
Other Utilities [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	2.0	6.0	5.8	9.8
Operating income (loss)	(1.2)	0.2	(1.0)	(0.1)
Utilities Business [Member]
Segment Reporting Information [Line Items]
Operating revenues	736.4	703.3	1,675.7	1,551.0
Operating income (loss)	94.0	94.4	239.2	208.2
Income (loss) from continuing operations, net of tax	53.0	56.6	151.2	121.5
Income (loss) from discontinued operations, net of tax	0	0	0	0
Net income (loss) attributable to common shareowners	53.0	56.6	151.2	121.5
Non-Regulated [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	13.9	14.7	27.4	26.6
Operating income (loss)	9.3	8.8	18.3	15.7
Income (loss) from continuing operations, net of tax	9.1	9.3	18.9	17.3
Income (loss) from discontinued operations, net of tax	(0.3)	(0.6)	(0.3)	(3.6)
Net income (loss) attributable to common shareowners	$ 8.8	$ 8.7	$ 18.6	$ 13.7