Summary Of Significant Accounting Policies Summary Of Significant Accounting Policies (Schedule Of New Accounting Standards And Changes In Accounting Principles) (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	Dec. 31, 2012
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets	$ 0.0				$ 150.1				$ 0.0	$ 150.1
Total current assets	826.8				1,043.1				826.8	1,043.1
Deferred charges and other	14.6				21.5				14.6	21.5
Total other assets	1,803.0				1,737.1				1,803.0	1,737.1
Total assets	12,495.2				12,063.5				12,495.2	12,063.5	$ 11,092.5
Other current liabilities	296.6				262.4				296.6	262.4
Total current liabilities	1,359.3				1,214.7				1,359.3	1,214.7
Long-term debt, net (excluding current portion)	3,522.2				3,584.3				3,522.2	3,584.3
Deferred tax liabilities	2,381.2				2,321.1				2,381.2	2,321.1
Total other liabilities	3,689.6				3,624.0				3,689.6	3,624.0
Retained earnings	2,068.9				1,938.0				2,068.9	1,938.0
Total common equity	3,724.1				3,438.7				3,724.1	3,438.7	3,281.4	$ 3,134.9
Total equity	3,924.1				3,640.5				3,924.1	3,640.5
Total liabilities and equity	12,495.2				12,063.5				12,495.2	12,063.5
Income tax expense (benefit)									70.4	44.3	53.9
Net income									388.4	393.3	376.2
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
Deferred tax expense (benefit) and investment tax credits									114.2	55.2	108.3
Other									(5.4)	59.7	23.7
Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred charges and other					43.9					43.9
Total other assets					1,759.5					1,759.5
Total assets					12,085.9					12,085.9
Long-term debt, net (excluding current portion)					3,606.7					3,606.7
Total liabilities and equity					12,085.9					12,085.9
New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred charges and other					(22.4)					(22.4)
Total other assets					(22.4)					(22.4)
Total assets					(22.4)					(22.4)
Long-term debt, net (excluding current portion)					(22.4)					(22.4)
Total liabilities and equity					(22.4)					(22.4)
IPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets	0.0				104.0				0.0	104.0
Total current assets	396.4				555.2				396.4	555.2
Deferred charges and other	5.0				2.0				5.0	2.0
Total other assets	1,368.0				1,321.2				1,368.0	1,321.2
Total assets	6,709.1				6,450.2				6,709.1	6,450.2
Other current liabilities	69.5				64.6				69.5	64.6
Total current liabilities	531.1				705.9				531.1	705.9
Long-term debt, net (excluding current portion)	1,856.9				1,608.0				1,856.9	1,608.0
Deferred tax liabilities	1,378.0				1,370.3				1,378.0	1,370.3
Total other liabilities	2,125.8				2,152.0				2,125.8	2,152.0
Retained earnings	554.1				508.1				554.1	508.1	461.9	415.2
Total common equity	1,995.3				1,784.3				1,995.3	1,784.3	1,648.1	1,486.4
Total equity	2,195.3				1,984.3				2,195.3	1,984.3
Total liabilities and equity	6,709.1				6,450.2				6,709.1	6,450.2
Income tax expense (benefit)									(22.7)	(48.9)	(36.3)
Net income	8.0	119.1	19.0	50.1	21.4	104.6	20.5	45.3	196.2	191.8	188.3
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
Deferred tax expense (benefit) and investment tax credits									28.9	(11.5)	3.0
Other									43.0	36.6	(11.2)
IPL [Member] | Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets					104.9					104.9
Total current assets					556.1					556.1
Deferred charges and other					12.7					12.7
Total other assets					1,331.9					1,331.9
Total assets					6,461.8					6,461.8
Long-term debt, net (excluding current portion)					1,618.7					1,618.7
Deferred tax liabilities	1,346.7				1,341.4				1,346.7	1,341.4
Total other liabilities	2,094.5				2,123.1				2,094.5	2,123.1
Retained earnings	585.4				537.9				585.4	537.9	493.5	448.0
Total common equity	2,026.6				1,814.1				2,026.6	1,814.1
Total equity	2,226.6				2,014.1				2,226.6	2,014.1
Total liabilities and equity					6,461.8					6,461.8
Income tax expense (benefit)										(51.7)	(37.9)
Net income		120.0	19.2	50.4	22.6	105.1	20.9	46.0		194.6	189.9
Net income (loss) attributable to common shareowners		117.4	16.7	47.8	20.1	102.5	18.4	43.4		184.4	173.6
Deferred tax expense (benefit) and investment tax credits										(9.7)	4.2
Other										32.0	(14.0)
IPL [Member] | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets					(0.9)					(0.9)
Total current assets					(0.9)					(0.9)
Total assets					(0.9)					(0.9)
Deferred tax liabilities	31.3				28.9				31.3	28.9
Total other liabilities	31.3				28.9				31.3	28.9
Retained earnings	(31.3)				(29.8)				(31.3)	(29.8)	(31.6)	(32.8)
Total common equity	(31.3)				(29.8)				(31.3)	(29.8)
Total equity	(31.3)				(29.8)				(31.3)	(29.8)
Total liabilities and equity					(0.9)					(0.9)
Income tax expense (benefit)										2.8	1.6
Net income										(2.8)	(1.6)
Net income (loss) attributable to common shareowners										(2.8)	(1.6)
Deferred tax expense (benefit) and investment tax credits										(1.8)	(1.2)
Other										4.6	2.8
IPL [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred charges and other					(10.7)					(10.7)
Total other assets					(10.7)					(10.7)
Total assets					(10.7)					(10.7)
Long-term debt, net (excluding current portion)					(10.7)					(10.7)
Total liabilities and equity					(10.7)					(10.7)
WPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets	0.0				37.7				0.0	37.7
Total current assets	423.5				457.4				423.5	457.4
Deferred charges and other	9.1				18.9				9.1	18.9
Total other assets	434.5				415.3				434.5	415.3
Total assets	5,270.4				5,117.6				5,270.4	5,117.6
Other current liabilities	79.5				46.6				79.5	46.6
Total current liabilities	336.9				310.3				336.9	310.3
Long-term debt, net (excluding current portion)	1,533.9				1,532.5				1,533.9	1,532.5
Deferred tax liabilities	1,005.4				967.1				1,005.4	967.1
Total other liabilities	1,632.0				1,559.4				1,632.0	1,559.4
Retained earnings	731.1				681.7				731.1	681.7	622.2	565.9
Total common equity	1,756.3				1,706.9				1,756.3	1,706.9
Total equity	1,767.6				1,715.4				1,767.6	1,715.4	1,647.4	1,591.3
Total liabilities and equity	5,270.4				5,117.6				5,270.4	5,117.6
Income tax expense (benefit)									82.9	85.3	85.6
Net income	24.4	68.4	39.7	45.1	33.3	57.9	34.7	55.2	177.6	181.1	179.1
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
Deferred tax expense (benefit) and investment tax credits									77.6	82.6	89.8
Other									27.4	(9.0)	(21.6)
WPL [Member] | Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets					37.5					37.5
Total current assets					457.2					457.2
Deferred charges and other					29.7					29.7
Total other assets					426.1					426.1
Total assets					5,128.2					5,128.2
Other current liabilities	78.2								78.2
Total current liabilities	335.6								335.6
Long-term debt, net (excluding current portion)					1,543.3					1,543.3
Deferred tax liabilities	1,010.8				970.0				1,010.8	970.0
Total other liabilities	1,637.4				1,562.3				1,637.4	1,562.3
Retained earnings	727.0				678.6				727.0	678.6	617.2	557.6
Total common equity	1,752.2				1,703.8				1,752.2	1,703.8
Total equity	1,763.5				1,712.3				1,763.5	1,712.3
Total liabilities and equity					5,128.2					5,128.2
Income tax expense (benefit)										85.6	87.2
Net income		67.9	39.5	44.8	29.8	61.6	34.6	54.8		180.8	177.5
Net income (loss) attributable to common shareowners		$ 67.5	$ 39.0	$ 44.6	29.1	$ 61.6	$ 34.6	$ 54.8		180.1	175.9
Deferred tax expense (benefit) and investment tax credits										80.7	86.5
Other										(6.8)	(16.7)
WPL [Member] | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax assets					0.2					0.2
Total current assets					0.2					0.2
Total assets					0.2					0.2
Other current liabilities	1.3								1.3
Total current liabilities	1.3								1.3
Deferred tax liabilities	(5.4)				(2.9)				(5.4)	(2.9)
Total other liabilities	(5.4)				(2.9)				(5.4)	(2.9)
Retained earnings	4.1				3.1				4.1	3.1	5.0	$ 8.3
Total common equity	4.1				3.1				4.1	3.1
Total equity	$ 4.1				3.1				$ 4.1	3.1
Total liabilities and equity					0.2					0.2
Income tax expense (benefit)										(0.3)	(1.6)
Net income										0.3	1.6
Net income (loss) attributable to common shareowners										0.3	1.6
Deferred tax expense (benefit) and investment tax credits										1.9	3.3
Other										(2.2)	$ (4.9)
WPL [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred charges and other					(10.8)					(10.8)
Total other assets					(10.8)					(10.8)
Total assets					(10.8)					(10.8)
Long-term debt, net (excluding current portion)					(10.8)					(10.8)
Total liabilities and equity					$ (10.8)					$ (10.8)