Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Segment Reporting Information [Line Items]
Operating revenues		$ 853.9	$ 843.8
Operating income (loss)		142.9	145.9
Income from continuing operations, net of tax		99.0	97.6
Income (loss) from discontinued operations, net of tax		1.4	(1.1)
Net income attributable to common shareowners		100.4	96.5
IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		450.5	458.7
Operating income (loss)		49.6	62.0
Net income attributable to common shareowners		37.2	45.6
WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		393.1	375.6
Operating income (loss)		86.0	78.8
Net income attributable to common shareowners		45.5	46.5
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	[1]	677.6	668.9
Operating income (loss)	[1]	107.2	109.8
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		356.2	361.6
Operating income (loss)		33.8	43.4
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		321.4	307.3
Operating income (loss)		73.4	66.4
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	[1]	154.3	152.2
Operating income (loss)	[1]	28.0	28.8
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		83.1	84.2
Operating income (loss)		14.4	15.8
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		71.2	68.0
Operating income (loss)		13.6	13.0
Other Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	[1]	11.7	13.2
Operating income (loss)	[1]	0.4	2.2
Other Utilities [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		11.2	12.9
Operating income (loss)		1.4	2.8
Other Utilities [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		0.5	0.3
Operating income (loss)		(1.0)	(0.6)
Utility Business [Member]
Segment Reporting Information [Line Items]
Operating revenues	[1]	843.6	834.3
Operating income (loss)	[1]	135.6	140.8
Income from continuing operations, net of tax	[1]	89.6	92.1
Income (loss) from discontinued operations, net of tax	[1]	0.0	0.0
Net income attributable to common shareowners	[1]	89.6	92.1
Non-Regulated [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		10.3	9.5
Operating income (loss)		7.3	5.1
Income from continuing operations, net of tax		9.4	5.5
Income (loss) from discontinued operations, net of tax		1.4	(1.1)
Net income attributable to common shareowners		$ 10.8	$ 4.4

[1] Alliant Energy’s utility business segments include: a) utility electric operations, which include Alliant Energy’s entire investment in ATC; b) utility gas operations; and c) utility other, which includes steam operations and the unallocated portions of the utility business.