Segments Of Business (Schedule Of Segment Of Business) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues	$ 880.1	$ 990.2	$ 790.2	$ 987.2	$ 873.5	$ 928.6	$ 816.1	$ 916.3	$ 3,647.7	$ 3,534.5	$ 3,382.2
Depreciation and amortization									567.2	506.9	461.8
Operating income (loss)	160.9	290.2	149.8	176.8	121.4	256.1	151.2	165.7	777.7	694.4	671.2
Interest expense									272.9	247.0	215.6
Equity income from unconsolidated investments, net									(53.0)	(54.6)	(44.8)
Income tax expense (benefit)									68.7	47.7	66.7
Net income attributable to common shareowners	111.5	226.0	94.6	125.1	85.3	205.5	100.4	120.9	557.2	512.1	457.3
Total assets	16,700.7				15,426.0				16,700.7	15,426.0	14,187.8
Investments in equity method subsidiaries	458.3				421.3				458.3	421.3	381.4
Construction and acquisition expenditures									1,640.1	1,633.9	1,466.9
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	496.8	596.5	441.2	555.1	494.1	547.6	474.8	525.8	2,089.6	2,042.3	1,870.3
Operating income (loss)	81.3	173.5	74.5	73.5	54.4	143.1	77.7	75.6	402.8	350.8	304.1
Interest expense									126.9	119.4	112.4
Income tax expense (benefit)									24.1	(3.2)	(10.9)
Net income attributable to common shareowners	44.7	141.1	45.0	53.3	39.1	126.5	51.7	46.7	284.1	264.0	216.8
Total assets	9,277.5				8,411.4				9,277.5	8,411.4
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	362.3	372.1	326.1	415.2	369.4	370.7	330.8	381.7	1,475.7	1,452.6	1,472.8
Operating income (loss)	73.8	$ 108.3	$ 67.0	$ 98.1	61.3	$ 104.2	$ 63.4	$ 84.0	347.2	312.9	333.7
Interest expense									102.2	97.8	93.8
Income tax expense (benefit)									49.3	36.2	61.9
Total assets	6,506.5				6,152.5				6,506.5	6,152.5
Electric [Member]
Segment Reporting Information [Line Items]
Revenues									3,063.6	3,000.3	2,894.7
Depreciation and amortization									512.7	457.3	412.0
Operating income (loss)									678.9	610.2	601.7
Equity income from unconsolidated investments, net									(1.4)	(0.9)	(0.7)
Total assets	13,659.0				12,486.3				13,659.0	12,486.3	11,396.2
Investments in equity method subsidiaries	9.5				8.1				9.5	8.1	8.3
Construction and acquisition expenditures									1,438.4	1,421.1	1,154.9
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues									1,781.2	1,731.1	1,598.9
Depreciation and amortization									294.9	254.7	215.1
Operating income (loss)									359.7	318.2	287.3
Total assets	8,074.6				7,219.9				8,074.6	7,219.9	6,524.4
Construction and acquisition expenditures									963.4	890.6	594.1
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues									1,282.4	1,269.2	1,295.8
Depreciation and amortization									217.8	202.6	196.9
Operating income (loss)									319.2	292.0	314.4
Total assets	5,584.4				5,266.4				5,584.4	5,266.4	4,871.8
Construction and acquisition expenditures									475.0	530.5	592.4
Gas [Member]
Segment Reporting Information [Line Items]
Revenues									455.2	446.6	400.9
Depreciation and amortization									46.4	42.0	38.2
Operating income (loss)									69.8	53.2	47.7
Equity income from unconsolidated investments, net									0.0	0.0	0.0
Total assets	1,268.5				1,184.4				1,268.5	1,184.4	1,199.8
Investments in equity method subsidiaries	0.0				0.0				0.0	0.0	0.0
Construction and acquisition expenditures									99.7	146.8	125.2
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues									264.2	266.2	226.0
Depreciation and amortization									28.6	25.2	22.2
Operating income (loss)									38.9	28.3	21.7
Total assets	733.8				687.5				733.8	687.5	727.9
Construction and acquisition expenditures									55.9	99.7	80.7
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues									191.0	180.4	174.9
Depreciation and amortization									17.8	16.8	16.0
Operating income (loss)									30.9	24.9	26.0
Total assets	534.7				496.9				534.7	496.9	471.9
Construction and acquisition expenditures									43.8	47.1	44.5
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues									46.5	48.0	47.5
Depreciation and amortization									3.2	3.6	7.7
Operating income (loss)									1.3	0.3	(11.6)
Equity income from unconsolidated investments, net									0.0	0.0	0.0
Total assets	856.5				893.2				856.5	893.2	766.5
Investments in equity method subsidiaries	0.0				0.0				0.0	0.0	0.0
Construction and acquisition expenditures									0.3	0.4	1.7
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues									44.2	45.0	45.4
Depreciation and amortization									3.2	3.6	7.7
Operating income (loss)									4.2	4.3	(4.9)
Total assets	469.1				504.0				469.1	504.0	353.7
Construction and acquisition expenditures									0.3	0.4	1.2
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues									2.3	3.0	2.1
Depreciation and amortization									0.0	0.0	0.0
Operating income (loss)									(2.9)	(4.0)	(6.7)
Total assets	387.4				389.2				387.4	389.2	412.8
Construction and acquisition expenditures									0.0	0.0	0.5
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues									3,565.3	3,494.9	3,343.1
Depreciation and amortization									562.3	502.9	457.9
Operating income (loss)									750.0	663.7	637.8
Interest expense									229.1	217.2	206.2
Equity income from unconsolidated investments, net									(1.4)	(0.9)	(0.7)
Income tax expense (benefit)									73.4	33.0	51.0
Net income attributable to common shareowners									517.1	472.1	403.4
Total assets	15,784.0				14,563.9				15,784.0	14,563.9	13,362.5
Investments in equity method subsidiaries	9.5				8.1				9.5	8.1	8.3
Construction and acquisition expenditures									1,538.4	1,568.3	1,281.8
Utility Business [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues									2,089.6	2,042.3	1,870.3
Depreciation and amortization									326.7	283.5	245.0
Operating income (loss)									402.8	350.8	304.1
Interest expense									126.9	119.4	112.4
Income tax expense (benefit)									24.1	(3.2)	(10.9)
Net income attributable to common shareowners									284.1	264.0	216.8
Total assets	9,277.5				8,411.4				9,277.5	8,411.4	7,606.0
Construction and acquisition expenditures									1,019.6	990.7	676.0
Utility Business [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues									1,475.7	1,452.6	1,472.8
Depreciation and amortization									235.6	219.4	212.9
Operating income (loss)									347.2	312.9	333.7
Interest expense									102.2	97.8	93.8
Income tax expense (benefit)									49.3	36.2	61.9
Net income attributable to common shareowners									233.0	208.1	186.6
Total assets	6,506.5				6,152.5				6,506.5	6,152.5	5,756.5
Construction and acquisition expenditures									518.8	577.6	637.4
Non-Utility [Member]
Segment Reporting Information [Line Items]
Revenues									82.4	39.6	39.1
Depreciation and amortization									4.9	4.0	3.9
Operating income (loss)									27.7	30.7	33.4
Interest expense									43.8	29.8	9.4
Equity income from unconsolidated investments, net									(51.6)	(53.7)	(44.1)
Income tax expense (benefit)									(4.7)	14.7	15.7
Net income attributable to common shareowners									40.1	40.0	53.9
Total assets	916.7				862.1				916.7	862.1	825.3
Investments in equity method subsidiaries	$ 448.8				$ 413.2				448.8	413.2	373.1
Construction and acquisition expenditures									$ 101.7	$ 65.6	$ 185.1