Segments Of Business (Schedule Of Segment Of Business) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating revenues	$ 797.0	$ 924.6	$ 754.6	$ 843.8	$ 740.1	$ 898.9	$ 717.2	$ 897.4	$ 3,320.0	$ 3,253.6	$ 3,350.3
Depreciation and amortization									411.6	401.3	388.1
Operating income (loss)	99.9	162.6	128.6	145.9	79.2	235.9	109.0	152.9	537.0	577.0	543.6
Interest expense									196.2	187.1	180.6
Equity (income) loss from unconsolidated investments, net									(39.6)	(33.8)	(40.4)
Income tax expense (benefit)									59.4	70.4	44.3
Net income (loss) attributable to common shareowners	62.7	128.4	83.9	96.5	34.1	179.9	67.6	96.6	371.5	378.2	383.1
Total assets	13,373.8				12,495.2				13,373.8	12,495.2	12,063.5
Investments in equity method subsidiaries	326.0				302.9				326.0	302.9	296.6
Construction and acquisition expenditures									1,196.8	1,034.3	902.8
IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	434.5	516.2	411.0	458.7	398.7	504.6	382.2	489.0	1,820.4	1,774.5	1,848.1
Depreciation and amortization									210.8	207.2	197.5
Operating income (loss)	34.9	125.9	48.0	62.0	25.6	117.0	33.8	65.5	270.8	241.9	209.2
Interest expense									103.2	96.8	89.9
Income tax expense (benefit)									(5.9)	(22.7)	(48.9)
Net income (loss) attributable to common shareowners	24.0	114.1	31.9	45.6	5.5	116.5	16.5	47.5	215.6	186.0	181.6
Total assets	7,304.7				6,709.1				7,304.7	6,709.1
WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	352.2	397.0	334.3	375.6	330.7	382.6	324.7	397.1	1,459.1	1,435.1	1,449.1
Depreciation and amortization									192.5	184.3	181.2
Operating income (loss)	58.2	115.0	75.0	78.8	49.3	110.3	68.3	80.8	327.0	308.7	301.0
Interest expense									91.4	92.4	86.4
Equity (income) loss from unconsolidated investments, net									(39.8)	(35.1)	(42.8)
Income tax expense (benefit)									93.3	82.9	85.3
Net income (loss) attributable to common shareowners	31.7	$ 69.0	$ 43.2	$ 46.5	24.2	$ 68.0	$ 39.2	$ 44.9	190.4	176.3	180.4
Total assets	5,290.3				5,270.4				5,290.3	5,270.4
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues									2,875.5	2,770.5	2,713.6
Depreciation and amortization									367.0	358.6	347.0
Operating income (loss)									571.9	514.1	442.4
Equity (income) loss from unconsolidated investments, net									(39.8)	(35.1)	(42.8)
Total assets	11,040.5				10,211.3				11,040.5	10,211.3	9,660.4
Investments in equity method subsidiaries	325.3				302.0				325.3	302.0	294.3
Construction and acquisition expenditures									1,005.5	855.8	774.8
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,569.7	1,503.8	1,493.3
Depreciation and amortization									189.4	187.9	178.7
Operating income (loss)									252.0	218.8	166.8
Total assets	6,278.2				5,754.1				6,278.2	5,754.1	5,398.3
Construction and acquisition expenditures									598.1	561.2	490.0
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,305.8	1,266.7	1,220.3
Depreciation and amortization									177.6	170.7	168.3
Operating income (loss)									319.9	295.3	275.6
Equity (income) loss from unconsolidated investments, net									(39.8)	(35.1)	(42.8)
Total assets	4,444.7				4,457.2				4,444.7	4,457.2	4,262.1
Investments in equity method subsidiaries	7.7				302.0				7.7	302.0	294.3
Construction and acquisition expenditures									407.4	294.6	284.8
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues									355.4	381.2	517.5
Depreciation and amortization									34.2	31.1	29.9
Operating income (loss)									30.7	34.6	53.8
Equity (income) loss from unconsolidated investments, net									0.0	0.0	0.0
Total assets	1,091.1				939.3				1,091.1	939.3	913.5
Investments in equity method subsidiaries	0.0				0.0				0.0	0.0	0.0
Construction and acquisition expenditures									137.1	106.4	63.2
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									204.0	217.3	296.5
Depreciation and amortization									19.3	17.5	17.0
Operating income (loss)									15.5	17.7	25.7
Total assets	653.3				548.2				653.3	548.2	544.1
Construction and acquisition expenditures									91.5	56.7	35.1
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									151.4	163.9	221.0
Depreciation and amortization									14.9	13.6	12.9
Operating income (loss)									15.2	16.9	28.1
Equity (income) loss from unconsolidated investments, net									0.0	0.0	0.0
Total assets	437.8				391.1				437.8	391.1	369.4
Investments in equity method subsidiaries	0.0				0.0				0.0	0.0	0.0
Construction and acquisition expenditures									45.6	49.7	28.1
Other Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues									48.6	57.9	66.1
Depreciation and amortization									2.1	1.8	1.8
Operating income (loss)									(4.8)	1.9	14.0
Equity (income) loss from unconsolidated investments, net									0.0	0.0	0.0
Total assets	781.0				828.9				781.0	828.9	993.9
Investments in equity method subsidiaries	0.0				0.0				0.0	0.0	0.0
Construction and acquisition expenditures									0.1	1.4	0.9
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									46.7	53.4	58.3
Depreciation and amortization									2.1	1.8	1.8
Operating income (loss)									3.3	5.4	16.7
Total assets	373.2				406.8				373.2	406.8	507.8
Construction and acquisition expenditures									0.1	1.4	0.9
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1.9	4.5	7.8
Depreciation and amortization									0.0	0.0	0.0
Operating income (loss)									(8.1)	(3.5)	(2.7)
Equity (income) loss from unconsolidated investments, net									0.0	0.0	0.0
Total assets	407.8				422.1				407.8	422.1	486.1
Investments in equity method subsidiaries	0.0				0.0				0.0	0.0	0.0
Construction and acquisition expenditures									0.0	0.0	0.0
Utility Business [Member]
Segment Reporting Information [Line Items]
Operating revenues									3,279.5	3,209.6	3,297.2
Depreciation and amortization									403.3	391.5	378.7
Operating income (loss)									597.8	550.6	510.2
Interest expense									194.6	189.2	176.3
Equity (income) loss from unconsolidated investments, net									(39.8)	(35.1)	(42.8)
Income tax expense (benefit)									87.4	60.2	36.4
Net income (loss) attributable to common shareowners									406.0	362.3	362.0
Total assets	12,912.6				11,979.5				12,912.6	11,979.5	11,567.8
Investments in equity method subsidiaries	325.3				302.0				325.3	302.0	294.3
Construction and acquisition expenditures									1,142.7	963.6	838.9
Utility Business [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,820.4	1,774.5	1,848.1
Depreciation and amortization									210.8	207.2	197.5
Operating income (loss)									270.8	241.9	209.2
Interest expense									103.2	96.8	89.9
Income tax expense (benefit)									(5.9)	(22.7)	(48.9)
Net income (loss) attributable to common shareowners									215.6	186.0	181.6
Total assets	7,304.7				6,709.1				7,304.7	6,709.1	6,450.2
Construction and acquisition expenditures									689.7	619.3	526.0
Utility Business [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,459.1	1,435.1	1,449.1
Depreciation and amortization									192.5	184.3	181.2
Operating income (loss)									327.0	308.7	301.0
Interest expense									91.4	92.4	86.4
Equity (income) loss from unconsolidated investments, net									(39.8)	(35.1)	(42.8)
Income tax expense (benefit)									93.3	82.9	85.3
Net income (loss) attributable to common shareowners									190.4	176.3	180.4
Total assets	5,290.3				5,270.4				5,290.3	5,270.4	5,117.6
Investments in equity method subsidiaries	7.7				302.0				7.7	302.0	294.3
Construction and acquisition expenditures									453.0	344.3	312.9
Non-Regulated [Member]
Segment Reporting Information [Line Items]
Operating revenues									40.5	44.0	53.1
Depreciation and amortization									8.3	9.8	9.4
Operating income (loss)									(60.8)	26.4	33.4
Interest expense									1.6		4.3
Interest income										(2.1)
Equity (income) loss from unconsolidated investments, net									0.2	1.3	2.4
Income tax expense (benefit)									(28.0)	10.2	7.9
Net income (loss) attributable to common shareowners									(34.5)	15.9	21.1
Total assets	461.2				515.7				461.2	515.7	495.7
Investments in equity method subsidiaries	$ 0.7				$ 0.9				0.7	0.9	2.3
Construction and acquisition expenditures									$ 54.1	$ 70.7	$ 63.9