CREDIT LOSSES - ROLLFORWARD OF ALLOWANCES (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 198.3	$ 220.1
Provision for credit losses	23.3	22.1
Provision for credit losses deferred for future recovery or refund	20.9	25.4
Write-offs charged against the allowance	(57.5)	(21.8)
Recovery of amounts previously written off	15.6	13.3
Balance at end of period	200.6	259.1
Change in allowance for credit losses	2.3
Utility Operations
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	198.3
Balance at end of period	200.6
Wisconsin | Utility Operations
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	84.0	102.1
Provision for credit losses	11.8	13.7
Write-offs charged against the allowance	(28.8)	(18.5)
Recovery of amounts previously written off	9.9	9.9
Balance at end of period	85.7	129.5
Wisconsin | Utility Operations | Uncollectible expense
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses deferred for future recovery or refund	8.8	22.3
Illinois | Utility Operations
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	105.5	111.6
Provision for credit losses	11.3	7.1
Write-offs charged against the allowance	(27.3)	(2.8)
Recovery of amounts previously written off	5.4	3.0
Balance at end of period	107.0	122.0
Illinois | Utility Operations | Uncollectible expense
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses deferred for future recovery or refund	12.1	3.1
Other States | Utility Operations
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	8.8	6.4
Provision for credit losses	0.2	1.3
Write-offs charged against the allowance	(1.4)	(0.5)
Recovery of amounts previously written off	0.3	0.4
Balance at end of period	7.9	7.6
Other States | Utility Operations | Uncollectible expense
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses deferred for future recovery or refund	$ 0.0	$ 0.0