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, 2014	$ 3,438.7	$ 1,784.3		$ 2.2	$ 33.4	$ 66.2	$ 1,508.0	$ 1,242.8	$ 959.0	$ 1,938.0	$ 508.1	$ 681.7	$ (0.6)	$ (8.9)	$ 8.5
Beginning 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)	(140.0)	(126.9)							(247.3)	(140.0)	(126.9)
Common stock issued, net	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	1,995.3		2.3	33.4	66.2	1,661.8	1,407.8	959.0	2,068.9	554.1	731.1	(0.4)	(8.5)	11.3
Ending balance at Dec. 31, 2015			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)	(151.9)	(135.0)							(266.5)	(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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common shareowners	457.3	216.8	186.6							457.3	216.8	186.6
Net income	467.5	227.0	186.6
Common stock dividends	(288.3)	(156.1)	(125.9)							(288.3)	(156.1)	(125.9)
Common stock issued, net	149.6						149.6
Capital contributions from parent		200.0	90.0					200.0	90.0
Transfer of investment in ATC to ATI			0.0
Other	1.7						2.8							(1.1)
Other comprehensive income (loss), net of tax	(0.1)	0.0	0.0										(0.1)
Ending balance at Dec. 31, 2017	4,182.2	2,509.7	1,881.5	$ 2.3	$ 33.4	$ 66.2	$ 1,845.5	$ 1,797.8	$ 1,109.0	$ 2,346.0	$ 678.5	$ 706.3	$ (0.5)	$ (11.1)	$ 0.0
Ending balance at Dec. 31, 2017	$ 4,382.2	$ 2,709.7	$ 1,881.5