Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Operating revenues:
Electric utility	$ 675.9	$ 640.4	$ 1,344.8	$ 1,311.7
Gas utility	57.0	51.7	209.2	250.1
Other utility	12.4	14.8	25.6	31.2
Non-regulated	9.3	10.3	18.8	21.6
Total operating revenues	754.6	717.2	1,598.4	1,614.6
Operating expenses:
Electric production fuel and purchased power	199.5	185.2	400.4	401.1
Electric transmission service	130.3	116.9	258.2	240.1
Cost of gas sold	24.6	21.9	119.8	152.7
Other operation and maintenance	144.5	157.3	289.6	305.2
Depreciation and amortization	102.1	100.4	204.6	200.6
Taxes other than income taxes	25.0	26.5	51.3	53.0
Total operating expenses	626.0	608.2	1,323.9	1,352.7
Operating income	128.6	109.0	274.5	261.9
Interest expense and other:
Interest expense	48.0	46.5	96.0	93.1
Equity income from unconsolidated investments, net	(9.1)	(11.3)	(19.6)	(17.8)
Allowance for funds used during construction	(15.3)	(8.6)	(28.5)	(15.4)
Interest income and other	0.0	(0.2)	(0.2)	(0.3)
Total interest expense and other	23.6	26.4	47.7	59.6
Income from continuing operations before income taxes	105.0	82.6	226.8	202.3
Income tax expense (benefit)	18.1	11.2	39.7	31.7
Income from continuing operations, net of tax	86.9	71.4	187.1	170.6
Loss from discontinued operations, net of tax	(0.5)	(1.3)	(1.6)	(1.3)
Net income	86.4	70.1	185.5	169.3
Preferred dividend requirements of Interstate Power and Light Company	2.5	2.5	5.1	5.1
Net income (loss) attributable to common shareowners	$ 83.9	$ 67.6	$ 180.4	$ 164.2
Weighted average number of common shares outstanding (basic and diluted) (in shares)	227.0	226.2	226.9	224.2
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)	$ 0.37	$ 0.31	$ 0.80	$ 0.74
Loss from discontinued operations, net of tax (in dollars per share)	0.00	(0.01)	0.00	(0.01)
Net income (in dollars per share)	$ 0.37	$ 0.30	$ 0.80	$ 0.73
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	$ 84.4	$ 68.9	$ 182.0	$ 165.5
Loss from discontinued operations, net of tax	(0.5)	(1.3)	(1.6)	(1.3)
Net income (loss) attributable to common shareowners	$ 83.9	$ 67.6	$ 180.4	$ 164.2
Dividends declared per common share (in dollars per share)	$ 0.29375	$ 0.275	$ 0.5875	$ 0.55
IPL [Member]
Operating revenues:
Electric utility	$ 364.4	$ 339.4	$ 726.0	$ 702.0
Gas utility	34.5	29.8	118.7	141.0
Other utility	12.1	13.0	25.0	28.2
Total operating revenues	411.0	382.2	869.7	871.2
Operating expenses:
Electric production fuel and purchased power	100.4	90.5	199.8	200.6
Electric transmission service	88.3	77.9	174.8	161.8
Cost of gas sold	15.9	13.0	68.3	84.0
Other operation and maintenance	93.0	100.6	185.0	193.2
Depreciation and amortization	52.4	52.1	105.1	103.9
Taxes other than income taxes	13.0	14.3	26.7	28.4
Total operating expenses	363.0	348.4	759.7	771.9
Operating income	48.0	33.8	110.0	99.3
Interest expense and other:
Interest expense	25.0	23.9	49.9	48.0
Allowance for funds used during construction	(12.1)	(6.7)	(22.4)	(12.0)
Interest income and other	(0.1)	0.0	(0.1)	(0.1)
Total interest expense and other	12.8	17.2	27.4	35.9
Income from continuing operations before income taxes	35.2	16.6	82.6	63.4
Income tax expense (benefit)	0.8	(2.4)	0.0	(5.7)
Net income	34.4	19.0	82.6	69.1
Preferred dividend requirements of Interstate Power and Light Company	2.5	2.5	5.1	5.1
Net income (loss) attributable to common shareowners	31.9	16.5	77.5	64.0
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners	31.9	16.5	77.5	64.0
WPL [Member]
Operating revenues:
Electric utility	311.5	301.0	618.8	609.7
Gas utility	22.5	21.9	90.5	109.1
Other utility	0.3	1.8	0.6	3.0
Total operating revenues	334.3	324.7	709.9	721.8
Operating expenses:
Electric production fuel and purchased power	99.1	94.7	200.6	200.5
Electric transmission service	42.0	39.0	83.4	78.3
Cost of gas sold	8.7	8.9	51.5	68.7
Other operation and maintenance	50.9	56.7	103.0	110.7
Depreciation and amortization	47.4	45.8	94.8	91.8
Taxes other than income taxes	11.2	11.3	22.8	22.7
Total operating expenses	259.3	256.4	556.1	572.7
Operating income	75.0	68.3	153.8	149.1
Interest expense and other:
Interest expense	22.9	23.3	45.8	46.4
Equity income from unconsolidated investments, net	(9.0)	(11.3)	(19.7)	(19.1)
Allowance for funds used during construction	(3.2)	(1.9)	(6.1)	(3.4)
Interest income and other	(0.2)	(0.1)	(0.3)	0.0
Total interest expense and other	10.5	10.0	19.7	23.9
Income from continuing operations before income taxes	64.5	58.3	134.1	125.2
Income tax expense (benefit)	20.8	18.6	43.4	40.4
Net income	43.7	39.7	90.7	84.8
Net income attributable to noncontrolling interest	0.5	0.5	1.0	0.7
Net income (loss) attributable to common shareowners	43.2	39.2	89.7	84.1
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners	$ 43.2	$ 39.2	$ 89.7	$ 84.1