Valuation And Qualifying Accounts and Reserves (Details) - Accumulated Provision for Uncollectible Accounts [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[1]	$ 10.5	$ 12.0	$ 8.7
Charged to Expense	[1]	17.3	21.2	15.1
Charged to Other Accounts	[1],[2]	2.4	1.0	5.4
Deductions	[1],[3]	22.9	23.7	17.2
Ending Balance	[1]	7.3	10.5	12.0
IPL [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	[1]	3.1	1.3	1.1
Charged to Expense	[1]	16.5	20.9	14.9
Charged to Other Accounts	[1],[2]	0.0	0.0	0.0
Deductions	[1],[3]	18.4	19.1	14.7
Ending Balance	[1]	1.2	3.1	1.3
WPL [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance		7.4	10.7	7.1
Charged to Expense		0.8	0.3	0.2
Charged to Other Accounts	[2]	2.4	1.0	5.4
Deductions	[3]	4.5	4.6	2.0
Ending Balance		$ 6.1	$ 7.4	$ 10.7

[1] Refer to Note 5(b) for discussion of IPL’s sales of accounts receivable program.

[2] Accumulated provision for uncollectible accounts: In accordance with its regulatory treatment, certain amounts provided by WPL are recorded in regulatory assets. WPL expenses these amounts when an uncollectible account is written-off. Accumulated provision for other reserves: In 2017, Alliant Energy recorded amounts to deferred tax liabilities related to the impacts of Federal Tax Reform.

[3] Deductions are of the nature for which the reserves were created. In the case of the accumulated provision for uncollectible accounts, deductions from this reserve are reduced by recoveries of amounts previously written off.