Segments Of Business (Schedule Of Segment Of Business) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues	$ 873.5	$ 928.6	$ 816.1	$ 916.3	$ 856.1	$ 906.9	$ 765.3	$ 853.9	$ 3,534.5	$ 3,382.2	$ 3,320.0
Depreciation and amortization									506.9	461.8	411.6
Operating income (loss)	121.4	256.1	151.2	165.7	134.0	236.3	153.7	147.2	694.4	671.2	554.1
Interest expense									247.0	215.6	196.2
Equity (income) loss from unconsolidated investments, net									(54.6)	(44.8)	(39.6)
Income tax expense (benefit)									47.7	66.7	59.4
Net income (loss) attributable to common shareowners	85.3	205.5	100.4	120.9	93.8	168.8	94.3	100.4	512.1	457.3	371.5
Total assets	15,426.0				14,187.8				15,426.0	14,187.8	13,373.8
Investments in equity method subsidiaries	421.3				381.4				421.3	381.4	326.0
Construction and acquisition expenditures									1,633.9	1,466.9	1,196.8
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	494.1	547.6	474.8	525.8	472.2	527.4	420.2	450.5	2,042.3	1,870.3	1,820.4
Depreciation and amortization									283.5	245.0	210.8
Operating income (loss)	54.4	143.1	77.7	75.6	50.9	133.8	68.1	51.3	350.8	304.1	277.6
Interest expense									119.4	112.4	103.2
Income tax expense (benefit)									(3.2)	(10.9)	(5.9)
Net income (loss) attributable to common shareowners	39.1	126.5	51.7	46.7	16.4	120.4	42.8	37.2	264.0	216.8	215.6
Total assets	8,411.4				7,606.0				8,411.4	7,606.0
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	369.4	370.7	330.8	381.7	374.7	370.2	334.8	393.1	1,452.6	1,472.8	1,459.1
Depreciation and amortization									219.4	212.9	192.5
Operating income (loss)	61.3	104.2	63.4	84.0	75.4	93.5	76.2	88.6	312.9	333.7	337.2
Interest expense									97.8	93.8	91.4
Equity (income) loss from unconsolidated investments, net									(0.9)	(0.7)	(39.8)
Income tax expense (benefit)									36.2	61.9	93.3
Net income (loss) attributable to common shareowners	38.0	$ 76.3	$ 39.8	$ 54.0	53.2	$ 49.8	$ 38.1	$ 45.5	208.1	186.6	190.4
Total assets	6,152.5				5,756.5				6,152.5	5,756.5
Electric [Member]
Segment Reporting Information [Line Items]
Revenues									3,000.3	2,894.7	2,875.5
Depreciation and amortization									457.3	412.0	367.0
Operating income (loss)									610.2	601.7	586.5
Equity (income) loss from unconsolidated investments, net									(0.9)	(0.7)	(0.7)
Total assets	12,486.3				11,396.2				12,486.3	11,396.2	10,722.9
Investments in equity method subsidiaries	8.1				8.3				8.1	8.3	7.7
Construction and acquisition expenditures									1,421.1	1,154.9	994.0
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues									1,731.1	1,598.9	1,569.7
Depreciation and amortization									254.7	215.1	189.4
Operating income (loss)									318.2	287.3	257.8
Total assets	7,219.9				6,524.4				7,219.9	6,524.4	6,278.2
Construction and acquisition expenditures									890.6	594.1	598.1
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues									1,269.2	1,295.8	1,305.8
Depreciation and amortization									202.6	196.9	177.6
Operating income (loss)									292.0	314.4	328.7
Equity (income) loss from unconsolidated investments, net											(0.7)
Total assets	5,266.4				4,871.8				5,266.4	4,871.8	4,444.7
Construction and acquisition expenditures									530.5	592.4	395.9
Gas [Member]
Segment Reporting Information [Line Items]
Revenues									446.6	400.9	355.4
Depreciation and amortization									42.0	38.2	34.2
Operating income (loss)									53.2	47.7	33.0
Equity (income) loss from unconsolidated investments, net									0.0	0.0	0.0
Total assets	1,184.4				1,199.8				1,184.4	1,199.8	1,091.1
Investments in equity method subsidiaries	0.0				0.0				0.0	0.0	0.0
Construction and acquisition expenditures									146.8	125.2	137.1
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues									266.2	226.0	204.0
Depreciation and amortization									25.2	22.2	19.3
Operating income (loss)									28.3	21.7	16.4
Total assets	687.5				727.9				687.5	727.9	653.3
Construction and acquisition expenditures									99.7	80.7	91.5
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues									180.4	174.9	151.4
Depreciation and amortization									16.8	16.0	14.9
Operating income (loss)									24.9	26.0	16.6
Equity (income) loss from unconsolidated investments, net											0.0
Total assets	496.9				471.9				496.9	471.9	437.8
Construction and acquisition expenditures									47.1	44.5	45.6
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues									48.0	47.5	48.6
Depreciation and amortization									3.6	7.7	2.1
Operating income (loss)									0.3	(11.6)	(4.7)
Equity (income) loss from unconsolidated investments, net									0.0	0.0	0.0
Total assets	893.2				766.5				893.2	766.5	781.0
Investments in equity method subsidiaries	0.0				0.0				0.0	0.0	0.0
Construction and acquisition expenditures									0.4	1.7	0.1
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues									45.0	45.4	46.7
Depreciation and amortization									3.6	7.7	2.1
Operating income (loss)									4.3	(4.9)	3.4
Total assets	504.0				353.7				504.0	353.7	373.2
Construction and acquisition expenditures									0.4	1.2	0.1
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues									3.0	2.1	1.9
Depreciation and amortization									0.0	0.0	0.0
Operating income (loss)									(4.0)	(6.7)	(8.1)
Equity (income) loss from unconsolidated investments, net											(39.1)
Total assets	389.2				412.8				389.2	412.8	407.8
Construction and acquisition expenditures									0.0	0.5	11.5
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues									3,494.9	3,343.1	3,279.5
Depreciation and amortization									502.9	457.9	403.3
Operating income (loss)									663.7	637.8	614.8
Interest expense									217.2	206.2	194.6
Equity (income) loss from unconsolidated investments, net									(0.9)	(0.7)	(0.7)
Income tax expense (benefit)									33.0	51.0	71.4
Net income (loss) attributable to common shareowners									472.1	403.4	385.2
Total assets	14,563.9				13,362.5				14,563.9	13,362.5	12,595.0
Investments in equity method subsidiaries	8.1				8.3				8.1	8.3	7.7
Construction and acquisition expenditures									1,568.3	1,281.8	1,131.2
Utility Business [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues									2,042.3	1,870.3	1,820.4
Depreciation and amortization									283.5	245.0	210.8
Operating income (loss)									350.8	304.1	277.6
Interest expense									119.4	112.4	103.2
Income tax expense (benefit)									(3.2)	(10.9)	(5.9)
Net income (loss) attributable to common shareowners									264.0	216.8	215.6
Total assets	8,411.4				7,606.0				8,411.4	7,606.0	7,304.7
Construction and acquisition expenditures									990.7	676.0	689.7
Utility Business [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues									1,452.6	1,472.8	1,459.1
Depreciation and amortization									219.4	212.9	192.5
Operating income (loss)									312.9	333.7	337.2
Interest expense									97.8	93.8	91.4
Equity (income) loss from unconsolidated investments, net											(39.8)
Income tax expense (benefit)									36.2	61.9	93.3
Net income (loss) attributable to common shareowners									208.1	186.6	190.4
Total assets	6,152.5				5,756.5				6,152.5	5,756.5	5,290.3
Construction and acquisition expenditures									577.6	637.4	453.0
Non-Utility [Member]
Segment Reporting Information [Line Items]
Revenues									39.6	39.1	40.5
Depreciation and amortization									4.0	3.9	8.3
Operating income (loss)									30.7	33.4	(60.7)
Interest expense									29.8	9.4	1.6
Equity (income) loss from unconsolidated investments, net									(53.7)	(44.1)	(38.9)
Income tax expense (benefit)									14.7	15.7	(12.0)
Net income (loss) attributable to common shareowners									40.0	53.9	(13.7)
Total assets	862.1				825.3				862.1	825.3	778.8
Investments in equity method subsidiaries	$ 413.2				$ 373.1				413.2	373.1	318.3
Construction and acquisition expenditures									$ 65.6	$ 185.1	$ 65.6