Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues:
Electric utility	$ 743.4	$ 708.7
Gas utility	215.8	185.6
Other utility	11.1	13.2
Non-utility	16.9	8.8
Total revenues	987.2	916.3
Operating expenses:
Electric production fuel and purchased power	218.4	203.2
Electric transmission service	123.0	126.4
Cost of gas sold	121.6	111.2
Other operation and maintenance	181.2	162.4
Depreciation and amortization	136.9	120.4
Taxes other than income taxes	29.3	27.0
Total operating expenses	810.4	750.6
Operating income	176.8	165.7
Other (income) and deductions:
Interest expense	66.3	59.2
Equity income from unconsolidated investments, net	(10.9)	(21.3)
Allowance for funds used during construction	(25.4)	(14.9)
Other	4.0	2.4
Total other (income) and deductions	34.0	25.4
Income before income taxes	142.8	140.3
Income taxes	15.1	16.8
Net income	127.7	123.5
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6
Net income attributable to common shareowners	$ 125.1	$ 120.9
Weighted average number of common shares outstanding (basic) (in shares)	236.5	231.4
Weighted average number of common shares outstanding (diluted) (in shares)	236.6	231.4
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted) (in dollars per share)	$ 0.53	$ 0.52
IPL [Member]
Revenues:
Electric utility	$ 419.8	$ 405.7
Gas utility	124.6	108.1
Other utility	10.7	12.0
Total revenues	555.1	525.8
Operating expenses:
Electric production fuel and purchased power	128.9	114.6
Electric transmission service	87.7	90.8
Cost of gas sold	63.3	60.6
Other operation and maintenance	108.0	105.5
Depreciation and amortization	77.1	64.8
Taxes other than income taxes	16.6	13.9
Total operating expenses	481.6	450.2
Operating income	73.5	75.6
Other (income) and deductions:
Interest expense	29.4	29.8
Allowance for funds used during construction	(15.8)	(7.4)
Other	1.9	0.8
Total other (income) and deductions	15.5	23.2
Income before income taxes	58.0	52.4
Income taxes	2.1	3.1
Net income	55.9	49.3
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6
Net income attributable to common shareowners	53.3	46.7
WPL [Member]
Revenues:
Electric utility	323.6	303.0
Gas utility	91.2	77.5
Other utility	0.4	1.2
Total revenues	415.2	381.7
Operating expenses:
Electric production fuel and purchased power	89.5	88.6
Electric transmission service	35.3	35.6
Cost of gas sold	58.3	50.6
Other operation and maintenance	63.5	56.3
Depreciation and amortization	58.6	54.6
Taxes other than income taxes	11.9	12.0
Total operating expenses	317.1	297.7
Operating income	98.1	84.0
Other (income) and deductions:
Interest expense	25.8	24.7
Allowance for funds used during construction	(9.6)	(7.5)
Other	1.6	1.1
Total other (income) and deductions	17.8	18.3
Income before income taxes	80.3	65.7
Income taxes	14.6	11.7
Net income	65.7	54.0
Net income attributable to common shareowners	$ 65.7	$ 54.0