Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Operating revenues:
Electric utility		$ 864.3	$ 835.8	$ 2,209.1	$ 2,147.5
Gas utility		39.5	38.0	248.7	288.1
Other utility		9.4	13.4	35.0	44.6
Non-regulated		11.4	11.7	30.2	33.3
Total operating revenues		924.6	898.9	2,523.0	2,513.5
Operating expenses:
Electric production fuel and purchased power		245.9	245.8	646.3	646.9
Electric transmission service		138.6	127.6	396.8	367.7
Cost of gas sold		12.5	13.6	132.3	166.3
Asset valuation charges for Franklin County wind farm		86.4	0.0	86.4	0.0
Other operation and maintenance		148.6	151.1	438.2	456.3
Depreciation and amortization		104.1	99.3	308.7	299.9
Taxes other than income taxes		25.9	25.6	77.2	78.6
Total operating expenses		762.0	663.0	2,085.9	2,015.7
Operating income		162.6	235.9	437.1	497.8
Interest expense and other:
Interest expense		48.8	46.4	144.8	139.5
Equity income from unconsolidated investments, net		(9.2)	(11.1)	(28.8)	(28.9)
Allowance for funds used during construction		(15.8)	(9.7)	(44.3)	(25.1)
Interest income and other		(0.1)	(0.1)	(0.3)	(0.4)
Total interest expense and other		23.7	25.5	71.4	85.1
Income from continuing operations before income taxes		138.9	210.4	365.7	412.7
Income tax expense (benefit)		7.5	27.8	47.2	59.5
Income from continuing operations, net of tax		131.4	182.6	318.5	353.2
Loss from discontinued operations, net of tax		(0.4)	(0.1)	(2.0)	(1.4)
Net income		131.0	182.5	316.5	351.8
Preferred dividend requirements of Interstate Power and Light Company		2.6	2.6	7.7	7.7
Net income (loss) attributable to common shareowners		$ 128.4	$ 179.9	$ 308.8	$ 344.1
Weighted average number of common shares outstanding (basic and diluted) (in shares)	[1]	227.2	226.4	227.0	225.0
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted):
Income from continuing operations, net of tax (in dollars per share)	[1]	$ 0.57	$ 0.79	$ 1.37	$ 1.54
Loss from discontinued operations, net of tax (in dollars per share)	[1]	0.00	0.00	(0.01)	(0.01)
Net income (in dollars per share)	[1]	$ 0.57	$ 0.79	$ 1.36	$ 1.53
Amounts attributable to common shareowners:
Income from continuing operations, net of tax		$ 128.8	$ 180.0	$ 310.8	$ 345.5
Loss from discontinued operations, net of tax		(0.4)	(0.1)	(2.0)	(1.4)
Net income (loss) attributable to common shareowners		$ 128.4	$ 179.9	$ 308.8	$ 344.1
Dividends declared per common share (in dollars per share)	[1]	$ 0.29375	$ 0.275	$ 0.88125	$ 0.825
IPL [Member]
Operating revenues:
Electric utility		$ 483.2	$ 468.6	$ 1,209.2	$ 1,170.6
Gas utility		23.9	23.1	142.6	164.1
Other utility		9.1	12.9	34.1	41.1
Total operating revenues		516.2	504.6	1,385.9	1,375.8
Operating expenses:
Electric production fuel and purchased power		125.0	131.4	324.8	332.0
Electric transmission service		95.9	87.5	270.7	249.3
Cost of gas sold		8.0	9.4	76.3	93.4
Other operation and maintenance		94.8	94.3	279.8	287.5
Depreciation and amortization		52.7	51.2	157.8	155.1
Taxes other than income taxes		13.9	13.8	40.6	42.2
Total operating expenses		390.3	387.6	1,150.0	1,159.5
Operating income		125.9	117.0	235.9	216.3
Interest expense and other:
Interest expense		25.5	23.8	75.4	71.8
Allowance for funds used during construction		(13.8)	(7.3)	(36.2)	(19.3)
Interest income and other		0.0	0.1	(0.1)	0.0
Total interest expense and other		11.7	16.6	39.1	52.5
Income from continuing operations before income taxes		114.2	100.4	196.8	163.8
Income tax expense (benefit)		(2.5)	(18.7)	(2.5)	(24.4)
Net income		116.7	119.1	199.3	188.2
Preferred dividend requirements of Interstate Power and Light Company		2.6	2.6	7.7	7.7
Net income (loss) attributable to common shareowners		114.1	116.5	191.6	180.5
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners		114.1	116.5	191.6	180.5
WPL [Member]
Operating revenues:
Electric utility		381.1	367.2	999.9	976.9
Gas utility		15.6	14.9	106.1	124.0
Other utility		0.3	0.5	0.9	3.5
Total operating revenues		397.0	382.6	1,106.9	1,104.4
Operating expenses:
Electric production fuel and purchased power		120.9	114.4	321.5	314.9
Electric transmission service		42.7	40.1	126.1	118.4
Cost of gas sold		4.5	4.2	56.0	72.9
Other operation and maintenance		54.2	57.0	157.2	167.7
Depreciation and amortization		48.7	45.7	143.5	137.5
Taxes other than income taxes		11.0	10.9	33.8	33.6
Total operating expenses		282.0	272.3	838.1	845.0
Operating income		115.0	110.3	268.8	259.4
Interest expense and other:
Interest expense		22.9	23.1	68.7	69.5
Equity income from unconsolidated investments, net		(9.3)	(11.1)	(29.0)	(30.2)
Allowance for funds used during construction		(2.0)	(2.4)	(8.1)	(5.8)
Interest income and other		0.1	(0.3)	(0.2)	(0.3)
Total interest expense and other		11.7	9.3	31.4	33.2
Income from continuing operations before income taxes		103.3	101.0	237.4	226.2
Income tax expense (benefit)		33.7	32.6	77.1	73.0
Net income		69.6	68.4	160.3	153.2
Net income attributable to noncontrolling interest		0.6	0.4	1.6	1.1
Net income (loss) attributable to common shareowners		69.0	68.0	158.7	152.1
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners		$ 69.0	$ 68.0	$ 158.7	$ 152.1

[1] Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.