Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues:
Electric utility	$ 915.9	$ 861.2	$ 2,350.5	$ 2,296.2
Gas utility	41.5	44.8	322.5	299.0
Other utility	11.2	12.3	33.2	36.2
Non-utility	21.6	10.3	61.4	29.6
Total revenues	990.2	928.6	2,767.6	2,661.0
Operating expenses:
Electric production fuel and purchased power	218.5	227.8	601.7	639.5
Electric transmission service	127.5	129.1	362.9	375.2
Cost of gas sold	9.1	11.3	151.1	150.0
Other operation and maintenance	173.7	148.4	527.2	468.8
Depreciation and amortization	143.8	129.0	423.6	376.4
Taxes other than income taxes	27.4	26.9	84.3	78.1
Total operating expenses	700.0	672.5	2,150.8	2,088.0
Operating income	290.2	256.1	616.8	573.0
Other (income) and deductions:
Interest expense	68.3	63.3	203.8	183.8
Equity income from unconsolidated investments, net	(11.6)	(9.8)	(35.2)	(41.6)
Allowance for funds used during construction	(21.9)	(18.8)	(65.6)	(51.8)
Other	3.7	1.6	11.0	6.0
Total other (income) and deductions	38.5	36.3	114.0	96.4
Income before income taxes	251.7	219.8	502.8	476.6
Income tax expense (benefit)	23.1	11.7	49.4	42.1
Net income	228.6	208.1	453.4	434.5
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6	7.7	7.7
Net income attributable to common shareowners	$ 226.0	$ 205.5	$ 445.7	$ 426.8
Weighted average number of common shares outstanding (basic) (in shares)	239.1	235.2	237.7	232.9
Weighted average number of common shares outstanding (diluted) (in shares)	239.9	235.2	238.2	232.9
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic) (in dollars per share)	$ 0.95	$ 0.87	$ 1.88	$ 1.83
Earnings per weighted average common share attributable to Alliant Energy common shareowners (diluted) (in dollars per share)	$ 0.94	$ 0.87	$ 1.87	$ 1.83
IPL [Member]
Revenues:
Electric utility	$ 560.9	$ 509.2	$ 1,373.0	$ 1,337.0
Gas utility	24.8	26.7	187.8	177.0
Other utility	10.8	11.7	32.0	34.2
Total revenues	596.5	547.6	1,592.8	1,548.2
Operating expenses:
Electric production fuel and purchased power	126.8	122.5	339.0	354.0
Electric transmission service	91.8	92.8	256.9	268.0
Cost of gas sold	5.9	6.4	80.0	83.8
Other operation and maintenance	100.2	94.6	305.6	297.1
Depreciation and amortization	83.7	73.9	243.4	209.2
Taxes other than income taxes	14.6	14.3	46.4	39.7
Total operating expenses	423.0	404.5	1,271.3	1,251.8
Operating income	173.5	143.1	321.5	296.4
Other (income) and deductions:
Interest expense	31.7	30.4	92.6	90.6
Allowance for funds used during construction	(10.8)	(11.0)	(34.5)	(28.3)
Other	2.0	0.5	5.4	2.0
Total other (income) and deductions	22.9	19.9	63.5	64.3
Income before income taxes	150.6	123.2	258.0	232.1
Income tax expense (benefit)	6.9	(5.9)	10.9	(0.5)
Net income	143.7	129.1	247.1	232.6
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6	7.7	7.7
Net income attributable to common shareowners	141.1	126.5	239.4	224.9
WPL [Member]
Revenues:
Electric utility	355.0	352.0	977.5	959.2
Gas utility	16.7	18.1	134.7	122.0
Other utility	0.4	0.6	1.2	2.0
Total revenues	372.1	370.7	1,113.4	1,083.2
Operating expenses:
Electric production fuel and purchased power	91.7	105.3	262.7	285.5
Electric transmission service	35.7	36.3	106.0	107.2
Cost of gas sold	3.2	4.9	71.1	66.2
Other operation and maintenance	62.3	54.2	188.2	172.8
Depreciation and amortization	58.9	54.1	176.6	164.2
Taxes other than income taxes	12.0	11.7	35.4	35.7
Total operating expenses	263.8	266.5	840.0	831.6
Operating income	108.3	104.2	273.4	251.6
Other (income) and deductions:
Interest expense	25.4	24.2	77.3	73.5
Allowance for funds used during construction	(11.1)	(7.8)	(31.1)	(23.5)
Other	1.4	1.3	4.6	3.4
Total other (income) and deductions	15.7	17.7	50.8	53.4
Income before income taxes	92.6	86.5	222.6	198.2
Income tax expense (benefit)	17.1	10.2	39.4	28.1
Net income			183.2	170.1
Net income attributable to common shareowners	$ 75.5	$ 76.3	$ 183.2	$ 170.1