Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Operating revenues		$ 906.9	$ 924.6	$ 2,526.1	$ 2,523.0
Operating income (loss)		231.5	162.6	523.7	437.1
Income (loss) from continuing operations, net of tax		168.8	128.8	362.1	310.8
Income (loss) from discontinued operations, net of tax		0.0	(0.4)	1.4	(2.0)
Net income (loss) attributable to common shareowners		168.8	128.4	363.5	308.8
IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		527.4	516.2	1,398.1	1,385.9
Operating income (loss)		131.8	125.9	247.7	235.9
Net income (loss) attributable to common shareowners		120.4	114.1	200.4	191.6
WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		370.2	397.0	1,098.1	1,106.9
Operating income (loss)		90.7	115.0	250.4	268.8
Net income (loss) attributable to common shareowners		49.8	69.0	133.4	158.7
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	[1]	840.6	864.3	2,199.1	2,209.1
Operating income (loss)	[1]	232.6	244.2	475.4	473.3
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		489.0	483.2	1,217.6	1,209.2
Operating income (loss)		138.3	125.9	234.5	213.8
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		351.6	381.1	981.5	999.9
Operating income (loss)		94.3	118.3	240.9	259.5
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	[1]	45.8	39.5	262.7	248.7
Operating income (loss)	[1]	(2.4)	(3.7)	29.5	27.0
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		27.4	23.9	147.2	142.6
Operating income (loss)		(2.1)	(1.4)	14.7	15.3
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		18.4	15.6	115.5	106.1
Operating income (loss)		(0.3)	(2.3)	14.8	11.7
Other Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues	[1]	11.2	9.4	34.4	35.0
Operating income (loss)	[1]	(7.7)	0.4	(6.8)	4.4
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		11.0	9.1	33.3	34.1
Operating income (loss)		(4.4)	1.4	(1.5)	6.8
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues		0.2	0.3	1.1	0.9
Operating income (loss)		(3.3)	(1.0)	(5.3)	(2.4)
Utility Business [Member]
Segment Reporting Information [Line Items]
Operating revenues	[1]	897.6	913.2	2,496.2	2,492.8
Operating income (loss)	[1]	222.5	240.9	498.1	504.7
Income (loss) from continuing operations, net of tax	[1]		183.1	353.5	350.3
Income (loss) from discontinued operations, net of tax	[1]		0.0	0.0	0.0
Net income (loss) attributable to common shareowners	[1]	176.3	183.1	353.5	350.3
Non-Regulated [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		9.3	11.4	29.9	30.2
Operating income (loss)		9.0	(78.3)	25.6	(67.6)
Income (loss) from continuing operations, net of tax			(54.3)	8.6	(39.5)
Income (loss) from discontinued operations, net of tax			(0.4)	1.4	(2.0)
Net income (loss) attributable to common shareowners		$ (7.5)	$ (54.7)	$ 10.0	$ (41.5)

[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.