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]	Cumulative Preferred Stock [Member]	Cumulative Preferred Stock [Member] IPL [Member]
Beginning balance at Dec. 31, 2016				$ 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)	$ 200.0	$ 200.0
Beginning balance at Dec. 31, 2016	$ 4,062.0	$ 2,449.0	$ 1,730.8
Increase (Decrease) in Shareowners' Equity [Roll Forward]
Net income attributable to common shareowners	457.3	216.8								457.3	216.8
Net income	467.5	227.0	186.6									186.6
Common stock dividends	(288.3)	(156.1)	(125.9)							(288.3)	(156.1)	(125.9)
Equity forward settlements, At-the-market offering program and Shareowner Direct Plan issuances	149.6						149.6
Capital contribution from parent		200.0	90.0					200.0	90.0
Equity-based compensation plans and 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				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)	200.0	200.0
Ending balance at Dec. 31, 2017	4,382.2	2,709.7	1,881.5
Increase (Decrease) in Shareowners' Equity [Roll Forward]
Net income attributable to common shareowners	512.1	264.0								512.1	264.0
Net income	522.3	274.2	208.1									208.1
Common stock dividends	(312.2)	(168.0)	(140.1)							(312.2)	(168.0)	(140.1)
Equity forward settlements, At-the-market offering program and Shareowner Direct Plan issuances	196.6			0.1			196.5
Capital contribution from parent		425.0	200.0					425.0	200.0
Equity-based compensation plans and other	4.8						3.5							1.3
Other comprehensive income (loss), net of tax	2.2	0.0	0.0										2.2
Ending balance at Dec. 31, 2018	4,585.7	3,030.7	2,149.5	2.4	33.4	66.2	2,045.5	2,222.8	1,309.0	2,545.9	774.5	774.3	1.7	(9.8)	200.0	200.0
Ending balance at Dec. 31, 2018	4,785.7	3,230.7	2,149.5
Increase (Decrease) in Shareowners' Equity [Roll Forward]
Net income attributable to common shareowners	557.2	284.1								557.2	284.1
Net income	567.4	294.3	233.0									233.0
Common stock dividends	(337.7)	(168.0)	(143.9)							(337.7)	(168.0)	(143.9)
Equity forward settlements, At-the-market offering program and Shareowner Direct Plan issuances	390.3			0.1			390.2
Capital contribution from parent		125.0	125.0					125.0	125.0
Equity-based compensation plans and other	10.0						10.2							(0.2)
Other comprehensive income (loss), net of tax	(0.4)	0.0	0.0										(0.4)
Ending balance at Dec. 31, 2019	5,205.1	3,271.8	2,363.6	$ 2.5	$ 33.4	$ 66.2	$ 2,445.9	$ 2,347.8	$ 1,434.0	$ 2,765.4	$ 890.6	$ 863.4	$ 1.3	$ (10.0)	$ 200.0	$ 200.0
Ending balance at Dec. 31, 2019	$ 5,405.1	$ 3,471.8	$ 2,363.6