Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Electric utility	$ 708.7	$ 677.6
Gas utility	185.6	154.3
Other utility	13.2	11.7
Non-utility	8.8	10.3
Total revenues	916.3	853.9
Operating expenses:
Electric production fuel and purchased power	203.2	207.8
Electric transmission service	126.4	124.7
Cost of gas sold	111.2	92.2
Other operation and maintenance	162.4	148.6
Depreciation and amortization	120.4	107.0
Taxes other than income taxes	27.0	26.4
Total operating expenses	750.6	706.7
Operating income	165.7	147.2
Other (income) and deductions:
Interest expense	59.2	52.3
Equity income from unconsolidated investments, net	(21.3)	(11.5)
Allowance for funds used during construction	(14.9)	(17.0)
Other	2.4	4.2
Total other (income) and deductions	25.4	28.0
Income from continuing operations before income taxes	140.3	119.2
Income tax expense (benefit)	16.8	17.6
Income from continuing operations, net of tax	123.5	101.6
Income from discontinued operations, net of tax	0.0	1.4
Net income	123.5	103.0
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6
Net income attributable to common shareowners	$ 120.9	$ 100.4
Weighted average number of common shares outstanding (basic and diluted) (in shares)	231.4	227.6
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted):
Income from continuing operations, net of tax (basic and diluted) (in dollars per share)	$ 0.52	$ 0.43
Income from discontinued operations, net of tax (basic and diluted) (in dollars per share)	0.00	0.01
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted) (in dollars per share)	$ 0.52	$ 0.44
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	$ 120.9	$ 99.0
Income from discontinued operations, net of tax	0.0	1.4
Net income attributable to common shareowners	$ 120.9	$ 100.4
Dividends declared per common share (in dollars per share)	$ 0.335	$ 0.315
IPL [Member]
Revenues:
Electric utility	$ 405.7	$ 356.2
Gas utility	108.1	83.1
Other utility	12.0	11.2
Total revenues	525.8	450.5
Operating expenses:
Electric production fuel and purchased power	114.6	109.5
Electric transmission service	90.8	81.7
Cost of gas sold	60.6	47.8
Other operation and maintenance	105.5	93.2
Depreciation and amortization	64.8	53.6
Taxes other than income taxes	13.9	13.4
Total operating expenses	450.2	399.2
Operating income	75.6	51.3
Other (income) and deductions:
Interest expense	29.8	27.7
Allowance for funds used during construction	(7.4)	(14.3)
Other	0.8	1.8
Total other (income) and deductions	23.2	15.2
Income from continuing operations before income taxes	52.4	36.1
Income tax expense (benefit)	3.1	(3.7)
Net income	49.3	39.8
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6
Net income attributable to common shareowners	46.7	37.2
Amounts attributable to common shareowners:
Net income attributable to common shareowners	46.7	37.2
WPL [Member]
Revenues:
Electric utility	303.0	321.4
Gas utility	77.5	71.2
Other utility	1.2	0.5
Total revenues	381.7	393.1
Operating expenses:
Electric production fuel and purchased power	88.6	98.3
Electric transmission service	35.6	43.0
Cost of gas sold	50.6	44.4
Other operation and maintenance	56.3	54.4
Depreciation and amortization	54.6	52.4
Taxes other than income taxes	12.0	12.0
Total operating expenses	297.7	304.5
Operating income	84.0	88.6
Other (income) and deductions:
Interest expense	24.7	22.9
Allowance for funds used during construction	(7.5)	(2.7)
Other	1.1	2.5
Total other (income) and deductions	18.3	22.7
Income from continuing operations before income taxes	65.7	65.9
Income tax expense (benefit)	11.7	20.4
Net income	54.0	45.5
Net income attributable to common shareowners	54.0	45.5
Amounts attributable to common shareowners:
Net income attributable to common shareowners	$ 54.0	$ 45.5