Segments Of Business (Schedule Of Segment Of Business) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Operating revenues	$ 740.1	$ 898.9	$ 717.2	$ 897.4	$ 804.1	$ 843.1	$ 750.3	$ 952.8	$ 3,253.6	$ 3,350.3	$ 3,276.8
Depreciation and amortization									401.3	388.1	370.9
Operating income (loss)	79.2	235.9	109.0	152.9	91.3	194.8	103.3	154.2	577.0	543.6	533.9
Interest expense									187.1	180.6	172.8
Equity (income) loss from unconsolidated investments, net									(33.8)	(40.4)	(43.7)
Income tax expense (benefit)									70.4	44.3	53.9
Net income (loss) attributable to common shareowners	34.1	179.9	67.6	96.6	60.0	153.3	61.8	108.0	378.2	383.1	358.3
Total assets	12,495.2				12,063.5				12,495.2	12,063.5	11,092.5
Investments in equity method subsidiaries	302.9				296.6				302.9	296.6	281.4
Construction and acquisition expenditures									1,034.3	902.8	798.3
IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	398.7	504.6	382.2	489.0	431.1	476.2	411.9	528.9	1,774.5	1,848.1	1,818.8
Depreciation and amortization									207.2	197.5	191.1
Operating income (loss)	25.6	117.0	33.8	65.5	23.8	93.9	34.0	57.5	241.9	209.2	212.0
Interest expense									96.8	89.9	81.3
Income tax expense (benefit)									(22.7)	(48.9)	(36.3)
Net income (loss) attributable to common shareowners	5.5	116.5	16.5	47.5	18.9	102.0	18.0	42.7	186.0	181.6	172.0
Total assets	6,709.1				6,450.2				6,709.1	6,450.2
WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	330.7	382.6	324.7	397.1	359.8	354.4	324.5	410.4	1,435.1	1,449.1	1,406.3
Depreciation and amortization									184.3	181.2	172.2
Operating income (loss)	49.3	110.3	68.3	80.8	59.4	93.9	60.0	87.7	308.7	301.0	296.1
Interest expense									92.4	86.4	85.0
Equity (income) loss from unconsolidated investments, net									(35.1)	(42.8)	(43.7)
Income tax expense (benefit)									82.9	85.3	85.6
Net income (loss) attributable to common shareowners	24.2	$ 68.0	$ 39.2	$ 44.9	32.6	$ 57.9	$ 34.7	$ 55.2	176.3	180.4	177.5
Total assets	5,270.4				5,117.6				5,270.4	5,117.6
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues									2,770.5	2,713.6	2,689.0
Depreciation and amortization									358.6	347.0	333.0
Operating income (loss)									514.1	442.4	444.5
Equity (income) loss from unconsolidated investments, net									(35.1)	(42.8)	(43.7)
Total assets	10,211.3				9,660.4				10,211.3	9,660.4	9,018.6
Investments in equity method subsidiaries	302.0				294.3				302.0	294.3	279.1
Construction and acquisition expenditures									855.8	774.8	677.3
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,503.8	1,493.3	1,491.8
Depreciation and amortization									187.9	178.7	173.1
Operating income (loss)									218.8	166.8	173.1
Total assets	5,754.1				5,398.3				5,754.1	5,398.3	4,905.3
Construction and acquisition expenditures									561.2	490.0	365.4
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,266.7	1,220.3	1,197.2
Depreciation and amortization									170.7	168.3	159.9
Operating income (loss)									295.3	275.6	271.4
Equity (income) loss from unconsolidated investments, net									(35.1)	(42.8)	(43.7)
Total assets	4,457.2				4,262.1				4,457.2	4,262.1	4,113.3
Investments in equity method subsidiaries	302.0				294.3				302.0	294.3	279.1
Construction and acquisition expenditures									294.6	284.8	311.9
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues									381.2	517.5	464.8
Depreciation and amortization									31.1	29.9	28.8
Operating income (loss)									34.6	53.8	57.3
Equity (income) loss from unconsolidated investments, net									0.0	0.0	0.0
Total assets	939.3				913.5				939.3	913.5	859.3
Investments in equity method subsidiaries	0.0				0.0				0.0	0.0	0.0
Construction and acquisition expenditures									106.4	63.2	47.0
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									217.3	296.5	273.9
Depreciation and amortization									17.5	17.0	16.5
Operating income (loss)									17.7	25.7	29.8
Total assets	548.2				544.1				548.2	544.1	518.8
Construction and acquisition expenditures									56.7	35.1	27.5
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									163.9	221.0	190.9
Depreciation and amortization									13.6	12.9	12.3
Operating income (loss)									16.9	28.1	27.5
Equity (income) loss from unconsolidated investments, net									0.0	0.0	0.0
Total assets	391.1				369.4				391.1	369.4	340.5
Investments in equity method subsidiaries	0.0				0.0				0.0	0.0	0.0
Construction and acquisition expenditures									49.7	28.1	19.5
Other Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues									57.9	66.1	71.3
Depreciation and amortization									1.8	1.8	1.5
Operating income (loss)									1.9	14.0	6.3
Equity (income) loss from unconsolidated investments, net									0.0	0.0	0.0
Total assets	828.9				993.9				828.9	993.9	712.2
Investments in equity method subsidiaries	0.0				0.0				0.0	0.0	0.0
Construction and acquisition expenditures									1.4	0.9	7.3
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									53.4	58.3	53.1
Depreciation and amortization									1.8	1.8	1.5
Operating income (loss)									5.4	16.7	9.1
Total assets	406.8				507.8				406.8	507.8	369.8
Construction and acquisition expenditures									1.4	0.9	7.3
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									4.5	7.8	18.2
Depreciation and amortization									0.0	0.0	0.0
Operating income (loss)									(3.5)	(2.7)	(2.8)
Equity (income) loss from unconsolidated investments, net									0.0	0.0	0.0
Total assets	422.1				486.1				422.1	486.1	342.4
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									3,209.6	3,297.2	3,225.1
Depreciation and amortization									391.5	378.7	363.3
Operating income (loss)									550.6	510.2	508.1
Interest expense									189.2	176.3	166.3
Equity (income) loss from unconsolidated investments, net									(35.1)	(42.8)	(43.7)
Income tax expense (benefit)									60.2	36.4	49.3
Net income (loss) attributable to common shareowners									362.3	362.0	349.5
Total assets	11,979.5				11,567.8				11,979.5	11,567.8	10,590.1
Investments in equity method subsidiaries	302.0				294.3				302.0	294.3	279.1
Construction and acquisition expenditures									963.6	838.9	731.6
Utility Business [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,774.5	1,848.1	1,818.8
Depreciation and amortization									207.2	197.5	191.1
Operating income (loss)									241.9	209.2	212.0
Interest expense									96.8	89.9	81.3
Income tax expense (benefit)									(22.7)	(48.9)	(36.3)
Net income (loss) attributable to common shareowners									186.0	181.6	172.0
Total assets	6,709.1				6,450.2				6,709.1	6,450.2	5,793.9
Construction and acquisition expenditures									619.3	526.0	400.2
Utility Business [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,435.1	1,449.1	1,406.3
Depreciation and amortization									184.3	181.2	172.2
Operating income (loss)									308.7	301.0	296.1
Interest expense									92.4	86.4	85.0
Equity (income) loss from unconsolidated investments, net									(35.1)	(42.8)	(43.7)
Income tax expense (benefit)									82.9	85.3	85.6
Net income (loss) attributable to common shareowners									176.3	180.4	177.5
Total assets	5,270.4				5,117.6				5,270.4	5,117.6	4,796.2
Investments in equity method subsidiaries	302.0				294.3				302.0	294.3	279.1
Construction and acquisition expenditures									344.3	312.9	331.4
Non-Regulated [Member]
Segment Reporting Information [Line Items]
Operating revenues									44.0	53.1	51.7
Depreciation and amortization									9.8	9.4	7.6
Operating income (loss)									26.4	33.4	25.8
Interest (income) expense									(2.1)	4.3	6.5
Equity (income) loss from unconsolidated investments, net									1.3	2.4	0.0
Income tax expense (benefit)									10.2	7.9	4.6
Net income (loss) attributable to common shareowners									15.9	21.1	8.8
Total assets	515.7				495.7				515.7	495.7	502.4
Investments in equity method subsidiaries	$ 0.9				$ 2.3				0.9	2.3	2.3
Construction and acquisition expenditures									$ 70.7	$ 63.9	$ 66.7