Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
Electric utility	$ 726.3	$ 680.9	$ 1,435.0	$ 1,358.5
Gas utility	68.6	62.6	254.2	216.9
Other utility	10.7	11.5	23.9	23.2
Non-utility	10.5	10.3	19.3	20.6
Total revenues	816.1	765.3	1,732.4	1,619.2
Operating expenses:
Electric production fuel and purchased power	208.5	184.3	411.7	392.1
Electric transmission service	119.7	117.6	246.1	242.3
Cost of gas sold	27.5	28.3	138.7	120.5
Other operation and maintenance	158.0	140.7	320.4	289.3
Depreciation and amortization	127.0	115.0	247.4	222.0
Taxes other than income taxes	24.2	25.7	51.2	52.1
Total operating expenses	664.9	611.6	1,415.5	1,318.3
Operating income	151.2	153.7	316.9	300.9
Other (income) and deductions:
Interest expense	61.3	52.8	120.5	105.1
Equity income from unconsolidated investments, net	(10.5)	(11.3)	(31.8)	(22.8)
Allowance for funds used during construction	(18.1)	(10.1)	(33.0)	(27.1)
Other	2.0	4.3	4.4	8.5
Total other (income) and deductions	34.7	35.7	60.1	63.7
Income from continuing operations before income taxes	116.5	118.0	256.8	237.2
Income tax expense (benefit)	13.6	21.2	30.4	38.8
Income from continuing operations, net of tax	102.9	96.8	226.4	198.4
Income from discontinued operations, net of tax	0.0	0.0	0.0	1.4
Net income	102.9	96.8	226.4	199.8
Preferred dividend requirements of Interstate Power and Light Company	2.5	2.5	5.1	5.1
Net income attributable to common shareowners	$ 100.4	$ 94.3	$ 221.3	$ 194.7
Weighted average number of common shares outstanding (basic and diluted) (in shares)	232.0	229.0	231.7	228.3
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted):
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted) (in dollars per share)	$ 0.43	$ 0.41	$ 0.96	$ 0.85
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	$ 100.4	$ 94.3	$ 221.3	$ 193.3
Income from discontinued operations, net of tax	0.0	0.0	0.0	1.4
Net income attributable to common shareowners	$ 100.4	$ 94.3	$ 221.3	$ 194.7
Dividends declared per common share (in dollars per share)	$ 0.335	$ 0.315	$ 0.67	$ 0.63
IPL [Member]
Revenues:
Electric utility	$ 422.1	$ 372.4	$ 827.8	$ 728.6
Gas utility	42.2	36.7	150.3	119.8
Other utility	10.5	11.1	22.5	22.3
Total revenues	474.8	420.2	1,000.6	870.7
Operating expenses:
Electric production fuel and purchased power	116.9	98.0	231.5	207.5
Electric transmission service	84.4	75.1	175.2	156.8
Cost of gas sold	16.8	16.9	77.4	64.7
Other operation and maintenance	97.0	87.6	202.5	180.8
Depreciation and amortization	70.5	61.2	135.3	114.8
Taxes other than income taxes	11.5	13.3	25.4	26.7
Total operating expenses	397.1	352.1	847.3	751.3
Operating income	77.7	68.1	153.3	119.4
Other (income) and deductions:
Interest expense	30.4	27.9	60.2	55.6
Allowance for funds used during construction	(9.9)	(6.1)	(17.3)	(20.4)
Other	0.7	1.6	1.5	3.4
Total other (income) and deductions	21.2	23.4	44.4	38.6
Income from continuing operations before income taxes	56.5	44.7	108.9	80.8
Income tax expense (benefit)	2.3	(0.6)	5.4	(4.3)
Net income	54.2	45.3	103.5	85.1
Preferred dividend requirements of Interstate Power and Light Company	2.5	2.5	5.1	5.1
Net income attributable to common shareowners	51.7	42.8	98.4	80.0
Amounts attributable to common shareowners:
Net income attributable to common shareowners	51.7	42.8	98.4	80.0
WPL [Member]
Revenues:
Electric utility	304.2	308.5	607.2	629.9
Gas utility	26.4	25.9	103.9	97.1
Other utility	0.2	0.4	1.4	0.9
Total revenues	330.8	334.8	712.5	727.9
Operating expenses:
Electric production fuel and purchased power	91.6	86.3	180.2	184.6
Electric transmission service	35.3	42.5	70.9	85.5
Cost of gas sold	10.7	11.4	61.3	55.8
Other operation and maintenance	62.3	54.1	118.6	108.5
Depreciation and amortization	55.5	52.8	110.1	105.2
Taxes other than income taxes	12.0	11.5	24.0	23.5
Total operating expenses	267.4	258.6	565.1	563.1
Operating income	63.4	76.2	147.4	164.8
Other (income) and deductions:
Interest expense	24.6	23.1	49.3	46.0
Allowance for funds used during construction	(8.2)	(4.0)	(15.7)	(6.7)
Other	1.0	2.3	2.1	4.8
Total other (income) and deductions	17.4	21.4	35.7	44.1
Income from continuing operations before income taxes	46.0	54.8	111.7	120.7
Income tax expense (benefit)	6.2	16.7	17.9	37.1
Net income			93.8	83.6
Net income attributable to common shareowners	39.8	38.1	93.8	83.6
Amounts attributable to common shareowners:
Net income attributable to common shareowners	$ 39.8	$ 38.1	$ 93.8	$ 83.6