Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Electric utility	$ 3,000.3	$ 2,894.7	$ 2,875.5
Gas utility	446.6	400.9	355.4
Other utility	48.0	47.5	48.6
Non-utility	39.6	39.1	40.5
Total revenues	3,534.5	3,382.2	3,320.0
Operating expenses:
Electric production fuel and purchased power	855.0	818.1	854.0
Electric transmission service	495.7	480.9	527.9
Cost of gas sold	232.3	211.4	194.3
Asset valuation charges for Franklin County wind farm	0.0	0.0	86.4
Other operation and maintenance	645.8	633.2	589.4
Depreciation and amortization	506.9	461.8	411.6
Taxes other than income taxes	104.4	105.6	102.3
Total operating expenses	2,840.1	2,711.0	2,765.9
Operating income (loss)	694.4	671.2	554.1
Other (income) and deductions:
Interest expense	247.0	215.6	196.2
Equity (income) loss from unconsolidated investments, net	(54.6)	(44.8)	(39.6)
Allowance for funds used during construction	(75.6)	(49.7)	(62.5)
Other	7.6	17.3	16.6
Total other (income) and deductions	124.4	138.4	110.7
Income from continuing operations before income taxes	570.0	532.8	443.4
Income tax expense (benefit)	47.7	66.7	59.4
Income from continuing operations, net of tax	522.3	466.1	384.0
Income (loss) from discontinued operations, net of tax	0.0	1.4	(2.3)
Net income	522.3	467.5	381.7
Preferred dividend requirements of Interstate Power and Light Company	10.2	10.2	10.2
Net income attributable to common shareowners	$ 512.1	$ 457.3	$ 371.5
Weighted average number of common shares outstanding (basic and diluted) (in shares)	233.6	229.7	227.1
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)	$ 2.19	$ 1.99	$ 1.65
Loss from discontinued operations, net of tax (in dollars per share)	0.00	0.00	(0.01)
Net income (in dollars per share)	$ 2.19	$ 1.99	$ 1.64
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	$ 512.1	$ 455.9	$ 373.8
Income (loss) from discontinued operations, net of tax	0.0	1.4	(2.3)
Net income	512.1	457.3	371.5
IPL [Member]
Revenues:
Electric utility	1,731.1	1,598.9	1,569.7
Gas utility	266.2	226.0	204.0
Other utility	45.0	45.4	46.7
Total revenues	2,042.3	1,870.3	1,820.4
Operating expenses:
Electric production fuel and purchased power	469.0	443.6	430.5
Electric transmission service	352.9	310.4	359.7
Cost of gas sold	129.6	115.6	111.0
Other operation and maintenance	402.6	396.6	376.9
Depreciation and amortization	283.5	245.0	210.8
Taxes other than income taxes	53.9	55.0	53.9
Total operating expenses	1,691.5	1,566.2	1,542.8
Operating income (loss)	350.8	304.1	277.6
Other (income) and deductions:
Interest expense	119.4	112.4	103.2
Allowance for funds used during construction	(42.2)	(31.4)	(52.0)
Other	2.6	7.0	6.5
Total other (income) and deductions	79.8	88.0	57.7
Income from continuing operations before income taxes	271.0	216.1	219.9
Income tax expense (benefit)	(3.2)	(10.9)	(5.9)
Net income	274.2	227.0	225.8
Preferred dividend requirements of Interstate Power and Light Company	10.2	10.2	10.2
Net income attributable to common shareowners	264.0	216.8	215.6
Amounts attributable to common shareowners:
Net income	264.0	216.8	215.6
WPL [Member]
Revenues:
Electric utility	1,269.2	1,295.8	1,305.8
Gas utility	180.4	174.9	151.4
Other utility	3.0	2.1	1.9
Total revenues	1,452.6	1,472.8	1,459.1
Operating expenses:
Electric production fuel and purchased power	386.0	374.5	423.5
Electric transmission service	142.8	170.5	168.2
Cost of gas sold	102.7	95.8	83.3
Other operation and maintenance	241.6	238.5	209.6
Depreciation and amortization	219.4	212.9	192.5
Taxes other than income taxes	47.2	46.9	44.8
Total operating expenses	1,139.7	1,139.1	1,121.9
Operating income (loss)	312.9	333.7	337.2
Other (income) and deductions:
Interest expense	97.8	93.8	91.4
Equity (income) loss from unconsolidated investments, net	(0.9)	(0.7)	(39.8)
Allowance for funds used during construction	(33.4)	(18.3)	(10.5)
Other	5.1	10.4	10.0
Total other (income) and deductions	68.6	85.2	51.1
Income from continuing operations before income taxes	244.3	248.5	286.1
Income tax expense (benefit)	36.2	61.9	93.3
Net income	208.1	186.6	192.8
Net income attributable to noncontrolling interest	0.0	0.0	2.4
Net income attributable to common shareowners	208.1	186.6	190.4
Amounts attributable to common shareowners:
Net income	$ 208.1	$ 186.6	$ 190.4