Consolidated Statements of Common Equity - USD ($) $ in Millions	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]	Shares in Deferred Compensation Trust [Member]	Noncontrolling Interest [Member] WPL [Member]
Beginning balance at Dec. 31, 2012	$ 3,134.9	$ 1,486.4		$ 1.1	$ 33.4	$ 66.2	$ 1,511.2	$ 1,037.8	$ 959.2	$ 1,630.7	$ 415.2	$ 565.9	$ (0.8)	$ (7.3)	$ 0.0
Beginning balance at Dec. 31, 2012			$ 1,591.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners	358.3	172.0	177.5							358.3	172.0	177.5
Net income	376.2	188.3	179.1
Common stock dividends	(208.3)	(128.1)	(116.3)							(208.3)	(128.1)	(116.3)
Common stock issued, net	0.0
Capital contributions from parent		120.0						120.0
Preferred stock issuance costs	(5.4)	(5.4)					(5.4)	(5.4)
Other	1.3	3.2	(5.1)				2.0	0.4	(0.2)		2.8	(4.9)		(0.7)
Other comprehensive income (loss), net of tax	0.6	0.0	0.0										0.6
Ending balance at Dec. 31, 2013	3,281.4	1,648.1		1.1	33.4	66.2	1,507.8	1,152.8	959.0	1,780.7	461.9	622.2	(0.2)	(8.0)	0.0
Ending balance at Dec. 31, 2013			1,647.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners	383.1	181.6	180.4							383.1	181.6	180.4			0.7
Net income	393.3	191.8	181.1
Common stock dividends	(225.8)	(140.0)	(118.7)							(225.8)	(140.0)	(118.7)
Common stock issued, net	0.0
Capital contributions from parent		90.0						90.0
Contributions from noncontrolling interest			8.6												8.6
Distributions to noncontrolling interest			(0.8)												(0.8)
Other	0.4	4.6	(2.2)				1.3				4.6	(2.2)		(0.9)
Other comprehensive income (loss), net of tax	(0.4)	0.0	0.0										(0.4)
Ending balance at Dec. 31, 2014	3,438.7	1,784.3	1,706.9	1.1	33.4	66.2	1,509.1	1,242.8	959.0	1,938.0	508.1	681.7	(0.6)	(8.9)	8.5
Ending balance at Dec. 31, 2014	3,640.5	1,984.3	1,715.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners	378.2	186.0	176.3							378.2	186.0	176.3			1.3
Net income	388.4	196.2	177.6
Common stock dividends	(247.3)	(140.0)	(126.9)							(247.3)	(140.0)	(126.9)
Common stock issued, net	151.2						151.2
Capital contributions from parent		165.0						165.0
Contributions from noncontrolling interest			3.4												3.4
Distributions to noncontrolling interest			(1.9)												(1.9)
Other	3.1						2.7							0.4
Other comprehensive income (loss), net of tax	0.2	0.0	0.0										0.2
Ending balance at Dec. 31, 2015	3,724.1	1,995.3	1,756.3	$ 1.1	$ 33.4	$ 66.2	$ 1,663.0	$ 1,407.8	$ 959.0	$ 2,068.9	$ 554.1	$ 731.1	$ (0.4)	$ (8.5)	$ 11.3
Ending balance at Dec. 31, 2015	$ 3,924.1	$ 2,195.3	$ 1,767.6