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, 2013		$ 3,281.4	[1]	$ 1,648.1		$ 2.2	[1]	$ 33.4	$ 66.2	$ 1,506.7	[1]	$ 1,152.8	$ 959.0	$ 1,780.7	[1]	$ 461.9	$ 622.2	$ (0.2)	[1]	$ (8.0)	[1]	$ 0.0
Beginning 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)	[1]	(140.0)	(118.7)									(225.8)	[1]	(140.0)	(118.7)
Common stock issued, net		0.0
Capital contributions from parent				90.0	0.0							90.0
Contributions from noncontrolling interest					8.6																	8.6
Distributions to noncontrolling interest					(0.8)																	(0.8)
Transfer of investment in ATC to ATI					0.0
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]	1,784.3		2.2	[1]	33.4	66.2	1,508.0	[1]	1,242.8	959.0	1,938.0	[1]	508.1	681.7	(0.6)	[1]	(8.9)	[1]	8.5
Ending balance at Dec. 31, 2014					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)	[1]	(140.0)	(126.9)									(247.3)	[1]	(140.0)	(126.9)
Common stock issued, net	[1]	151.2				0.1				151.1
Capital contributions from parent				165.0	0.0							165.0
Contributions from noncontrolling interest					3.4																	3.4
Distributions to noncontrolling interest					(1.9)																	(1.9)
Transfer of investment in ATC to ATI					0.0
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]	1,995.3	1,756.3	2.3	[1]	33.4	66.2	1,661.8	[1]	1,407.8	959.0	2,068.9	[1]	554.1	731.1	(0.4)	[1]	(8.5)	[1]	11.3
Ending balance at Dec. 31, 2015		3,924.1		2,195.3	1,767.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners		371.5		215.6	190.4									371.5		215.6	190.4					2.4
Net income		381.7		225.8	192.8
Common stock dividends		(266.5)	[1]	(151.9)	(135.0)									(266.5)	[1]	(151.9)	(135.0)
Common stock issued, net		26.6								26.6
Capital contributions from parent				190.0	60.0							190.0	60.0
Contributions from noncontrolling interest					11.5																	11.5
Distributions to noncontrolling interest					(2.5)																	(2.5)
Transfer of investment in ATC to ATI					(163.6)												(140.9)					(22.7)
Other		6.3								4.7				3.1						(1.5)
Other comprehensive income (loss), net of tax		0.0		0.0	0.0
Ending balance at Dec. 31, 2016		3,862.0		2,249.0	1,730.8	$ 2.3		$ 33.4	$ 66.2	$ 1,693.1		$ 1,597.8	$ 1,019.0	$ 2,177.0		$ 617.8	$ 645.6	$ (0.4)		$ (10.0)		$ 0.0
Ending balance at Dec. 31, 2016		$ 4,062.0		$ 2,449.0	$ 1,730.8

[1] Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.