Segments Of Business (Schedule Of Segment Of Business) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating revenues	$ 804.1	$ 843.1	$ 750.3	$ 952.8	$ 832.6	$ 866.6	$ 718.0	$ 859.6	$ 3,350.3	$ 3,276.8	$ 3,094.5
Depreciation and amortization									388.1	370.9	332.4
Operating income (loss)	91.3	194.8	103.3	154.2	108.6	201.4	103.2	120.7	543.6	533.9	519.7
Interest expense									180.6	172.8	156.7
Equity (income) loss from unconsolidated investments, net									(40.4)	(43.7)	(41.3)
Income tax expense (benefit)									44.3	53.9	89.4
Net income (loss) attributable to common shareowners	60.0	153.3	61.8	108.0	65.5	157.6	65.3	69.9	383.1	358.3	319.8
Total assets	12,085.9				11,112.4				12,085.9	11,112.4	10,785.5
Investments in equity method subsidiaries	296.6				281.4				296.6	281.4	266.6
Construction and acquisition expenditures									902.8	798.3	1,158.1
IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	431.1	476.2	411.9	528.9	463.1	494.4	383.4	477.9	1,848.1	1,818.8	1,650.3
Depreciation and amortization									197.5	191.1	188.9
Operating income (loss)	23.8	93.9	34.0	57.5	36.2	100.0	34.7	41.1	209.2	212.0	200.3
Interest expense									89.9	81.3	78.5
Income tax expense (benefit)									(51.7)	(37.9)	(19.8)
Net income (loss) attributable to common shareowners	20.1	102.5	18.4	43.4	18.5	110.0	22.2	22.9	184.4	173.6	137.6
Total assets	6,461.8				5,806.0				6,461.8	5,806.0
WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues	359.8	354.4	324.5	410.4	355.7	360.9	319.9	369.8	1,449.1	1,406.3	1,392.0
Depreciation and amortization									181.2	172.2	140.9
Operating income (loss)	59.4	93.9	60.0	87.7	67.8	95.9	59.7	72.7	301.0	296.1	284.8
Interest expense									86.4	85.0	80.2
Equity (income) loss from unconsolidated investments, net									(42.8)	(43.7)	(42.1)
Income tax expense (benefit)									85.6	87.2	94.6
Net income (loss) attributable to common shareowners	29.1	61.6	34.6	54.8	38.2	61.3	34.4	42.0	180.1	175.9	162.4
Total assets	5,128.2				4,804.4				5,128.2	4,804.4
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues									2,713.6	2,689.0	2,589.3
Depreciation and amortization									347.0	333.0	299.3
Operating income (loss)									442.4	444.5	426.2
Equity (income) loss from unconsolidated investments, net									(42.8)	(43.7)	(42.1)
Total assets	9,660.4				9,018.6				9,660.4	9,018.6	8,438.8
Investments in equity method subsidiaries	294.3				279.1				294.3	279.1	264.3
Construction and acquisition expenditures									774.8	677.3	994.0
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,493.3	1,491.8	1,371.1
Depreciation and amortization									178.7	173.1	171.2
Operating income (loss)									166.8	173.1	166.2
Total assets	5,398.3				4,905.3				5,398.3	4,905.3	4,500.9
Construction and acquisition expenditures									490.0	365.4	291.0
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,220.3	1,197.2	1,218.2
Depreciation and amortization									168.3	159.9	128.1
Operating income (loss)									275.6	271.4	260.0
Equity (income) loss from unconsolidated investments, net									(42.8)	(43.7)	(42.1)
Total assets	4,262.1				4,113.3				4,262.1	4,113.3	3,937.9
Investments in equity method subsidiaries	294.3				279.1				294.3	279.1	264.3
Construction and acquisition expenditures									284.8	311.9	703.0
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues									517.5	464.8	396.3
Depreciation and amortization									29.9	28.8	29.1
Operating income (loss)									53.8	57.3	51.5
Equity (income) loss from unconsolidated investments, net									0	0	0
Total assets	913.5				859.3				913.5	859.3	814.8
Investments in equity method subsidiaries	0				0				0	0	0
Construction and acquisition expenditures									63.2	47.0	31.4
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									296.5	273.9	226.7
Depreciation and amortization									17.0	16.5	16.3
Operating income (loss)									25.7	29.8	24.2
Total assets	544.1				518.8				544.1	518.8	479.5
Construction and acquisition expenditures									35.1	27.5	16.4
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									221.0	190.9	169.6
Depreciation and amortization									12.9	12.3	12.8
Operating income (loss)									28.1	27.5	27.3
Equity (income) loss from unconsolidated investments, net									0	0	0
Total assets	369.4				340.5				369.4	340.5	335.3
Investments in equity method subsidiaries	0				0				0	0	0
Construction and acquisition expenditures									28.1	19.5	15.0
Other Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues									66.1	71.3	56.7
Depreciation and amortization									1.8	1.5	1.4
Operating income (loss)									14.0	6.3	7.4
Equity (income) loss from unconsolidated investments, net									0	0	0
Total assets	1,016.1				732.5				1,016.1	732.5	966.0
Investments in equity method subsidiaries	0				0				0	0	0
Construction and acquisition expenditures									0.9	7.3	0.1
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									58.3	53.1	52.5
Depreciation and amortization									1.8	1.5	1.4
Operating income (loss)									16.7	9.1	9.9
Total assets	519.4				381.9				519.4	381.9	476.6
Construction and acquisition expenditures									0.9	7.3	0.1
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									7.8	18.2	4.2
Depreciation and amortization									0	0	0
Operating income (loss)									(2.7)	(2.8)	(2.5)
Equity (income) loss from unconsolidated investments, net									0	0	0
Total assets	496.7				350.6				496.7	350.6	489.4
Investments in equity method subsidiaries	0				0				0	0	0
Construction and acquisition expenditures									0	0	0
Utility Business [Member]
Segment Reporting Information [Line Items]
Operating revenues									3,297.2	3,225.1	3,042.3
Depreciation and amortization									378.7	363.3	329.8
Operating income (loss)									510.2	508.1	485.1
Interest expense									176.3	166.3	158.7
Equity (income) loss from unconsolidated investments, net									(42.8)	(43.7)	(42.1)
Income tax expense (benefit)									33.9	49.3	74.8
Net income (loss) attributable to common shareowners									364.5	349.5	300.0
Total assets	11,590.0				10,610.4				11,590.0	10,610.4	10,219.6
Investments in equity method subsidiaries	294.3				279.1				294.3	279.1	264.3
Construction and acquisition expenditures									838.9	731.6	1,025.5
Utility Business [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,848.1	1,818.8	1,650.3
Depreciation and amortization									197.5	191.1	188.9
Operating income (loss)									209.2	212.0	200.3
Interest expense									89.9	81.3	78.5
Income tax expense (benefit)									(51.7)	(37.9)	(19.8)
Net income (loss) attributable to common shareowners									184.4	173.6	137.6
Total assets	6,461.8				5,806.0				6,461.8	5,806.0	5,457.0
Construction and acquisition expenditures									526.0	400.2	307.5
Utility Business [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,449.1	1,406.3	1,392.0
Depreciation and amortization									181.2	172.2	140.9
Operating income (loss)									301.0	296.1	284.8
Interest expense									86.4	85.0	80.2
Equity (income) loss from unconsolidated investments, net									(42.8)	(43.7)	(42.1)
Income tax expense (benefit)									85.6	87.2	94.6
Net income (loss) attributable to common shareowners									180.1	175.9	162.4
Total assets	5,128.2				4,804.4				5,128.2	4,804.4	4,762.6
Investments in equity method subsidiaries	294.3				279.1				294.3	279.1	264.3
Construction and acquisition expenditures									312.9	331.4	718.0
Non-Regulated [Member]
Segment Reporting Information [Line Items]
Operating revenues									53.1	51.7	52.2
Depreciation and amortization									9.4	7.6	2.6
Operating income (loss)									33.4	25.8	34.6
Interest expense									4.3	6.5	(2.0)
Equity (income) loss from unconsolidated investments, net									2.4	0	0.8
Income tax expense (benefit)									10.4	4.6	14.6
Net income (loss) attributable to common shareowners									18.6	8.8	19.8
Total assets	495.9				502.0				495.9	502.0	565.9
Investments in equity method subsidiaries	2.3				2.3				2.3	2.3	2.3
Construction and acquisition expenditures									$ 63.9	$ 66.7	$ 132.6