Consolidated Statements of Common Equity (USD $) In Millions, unless otherwise specified	Total	IPL [Member]	WPL [Member]	Common Stock [Member]	Common Stock [Member] IPL [Member]	Common Stock [Member] WPL [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] IPL [Member]	Additional Paid-in Capital [Member] WPL [Member]	Retained Earnings [Member]	Retained Earnings [Member] IPL [Member]	Retained Earnings [Member] WPL [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Deferred Compensation, Share-based Payments [Member]	Noncontrolling Interest [Member] WPL [Member]
Beginning balance at Dec. 31, 2011			$ 1,442.4
Beginning balance at Dec. 31, 2011	3,013.0	1,394.4		1.1	33.4	66.2	1,510.8	927.7	869.0	1,510.2	433.3	507.2	(0.8)	(8.3)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners	319.8	137.6	162.4							319.8	137.6	162.4
Net income	335.7	150.2	165.7
Common stock dividends	(199.3)	(122.9)	(112.0)							(199.3)	(122.9)	(112.0)
Capital contributions from parent		110.0	90.0					110.0	90.0
Other	1.4	0.1	0.2				0.4	0.1	0.2					1.0
Other comprehensive income, net of tax	0	0	0
Ending balance at Dec. 31, 2012			1,583.0
Ending balance at Dec. 31, 2012	3,134.9	1,519.2		1.1	33.4	66.2	1,511.2	1,037.8	959.2	1,630.7	448.0	557.6		(7.3)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners	69.9	22.9	42.0
Net income		31.5	43.6
Ending balance at Mar. 31, 2013
Beginning balance at Dec. 31, 2012			1,583.0
Beginning balance at Dec. 31, 2012	3,134.9	1,519.2		1.1	33.4	66.2	1,511.2	1,037.8	959.2	1,630.7	448.0	557.6	(0.8)	(7.3)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners	358.3	173.6	175.9							358.3	173.6	175.9
Net income	376.2	189.9	177.5
Common stock dividends	(208.3)	(128.1)	(116.3)							(208.3)	(128.1)	(116.3)
Capital contributions from parent		120.0	0					120.0
Preferred stock issuance costs	(5.4)	(5.4)					(5.4)	(5.4)
Other	1.3	0.4	(0.2)				2.0	0.4	(0.2)					(0.7)
Other comprehensive income, net of tax	0.6	0	0										0.6
Ending balance at Dec. 31, 2013	3,483.2	1,879.7	1,642.4
Ending balance at Dec. 31, 2013	3,281.4	1,679.7	1,642.4	1.1	33.4	66.2	1,507.8	1,152.8	959.0	1,780.7	493.5	617.2	(0.2)	(8.0)
Beginning balance at Sep. 30, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners	65.5	18.5	38.2
Net income		21.1	38.2
Ending balance at Dec. 31, 2013	3,483.2	1,879.7	1,642.4
Ending balance at Dec. 31, 2013	3,281.4	1,679.7	1,642.4	1.1	33.4	66.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners	108.0	43.4	54.8
Net income		46.0	54.8
Ending balance at Mar. 31, 2014
Beginning balance at Dec. 31, 2013	3,483.2	1,879.7	1,642.4
Beginning balance at Dec. 31, 2013	3,281.4	1,679.7	1,642.4	1.1	33.4	66.2	1,507.8	1,152.8		1,780.7	493.5	617.2	(0.2)	(8.0)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners	383.1	184.4	180.1							383.1	184.4	180.1			0.7
Net income	393.3	194.6	180.8
Common stock dividends	(225.8)	(140.0)	(118.7)							(225.8)	(140.0)	(118.7)
Capital contributions from parent		90.0	0					90.0
Other	0.4						1.3							(0.9)
Other comprehensive income, net of tax	(0.4)	0	0										(0.4)
Contributions from noncontrolling interest			8.6												8.6
Distributions to noncontrolling interest			(0.8)												(0.8)
Ending balance at Dec. 31, 2014	3,640.5	2,014.1	1,712.3
Ending balance at Dec. 31, 2014	3,438.7	1,814.1	1,703.8	1.1	33.4	66.2	1,509.1	1,242.8	959.0	1,938.0	537.9	678.6	(0.6)	(8.9)	8.5
Beginning balance at Sep. 30, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners	60.0	20.1	29.1
Net income		22.6	29.8
Ending balance at Dec. 31, 2014	3,640.5	2,014.1	1,712.3
Ending balance at Dec. 31, 2014	$ 3,438.7	$ 1,814.1	$ 1,703.8	$ 1.1	$ 33.4	$ 66.2			$ 959.0