CREDIT LOSSES - ROLLFORWARD OF ALLOWANCES (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 178.7	$ 175.8	$ 199.3	$ 198.3
Provision for credit losses	14.8	15.8	46.9	57.9
Write-offs charged against the allowance	(47.7)	(49.4)	(152.7)	(148.1)
Recovery of amounts previously written off	14.1	13.5	43.2	43.3
Balance at end of period	176.8	168.5	176.8	168.5
Change in allowance for credit losses			22.5	29.8
Uncollectible expense
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses deferred for future recovery or refund	16.9	12.8	40.1	17.1
Utility Operations
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period			199.3
Balance at end of period	176.8		176.8
Wisconsin | Utility Operations
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	76.4	78.0	82.0	84.0
Provision for credit losses	10.2	10.0	28.1	33.6
Write-offs charged against the allowance	(31.8)	(34.6)	(89.8)	(85.5)
Recovery of amounts previously written off	7.4	8.8	25.4	26.7
Balance at end of period	72.0	72.4	72.0	72.4
Wisconsin | Utility Operations | Uncollectible expense
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses deferred for future recovery or refund	9.8	10.2	26.3	13.6
Illinois | Utility Operations
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	97.0	91.0	111.0	105.5
Provision for credit losses	4.0	5.2	17.3	23.6
Write-offs charged against the allowance	(14.4)	(13.5)	(58.7)	(58.7)
Recovery of amounts previously written off	6.3	4.4	16.6	15.8
Balance at end of period	100.0	89.7	100.0	89.7
Illinois | Utility Operations | Uncollectible expense
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses deferred for future recovery or refund	7.1	2.6	13.8	3.5
Other States | Utility Operations
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	5.3	6.8	6.3	8.8
Provision for credit losses	0.6	0.6	1.5	0.7
Write-offs charged against the allowance	(1.5)	(1.3)	(4.2)	(3.9)
Recovery of amounts previously written off	0.4	0.3	1.2	0.8
Balance at end of period	4.8	6.4	4.8	6.4
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	$ 0.0	$ 0.0