CREDIT LOSSES - ROLLFORWARD OF ALLOWANCES (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 213.8	$ 200.6	$ 199.3	$ 198.3
Provision for credit losses	11.1	18.8	32.1	42.1
Write-offs charged against the allowance	(51.5)	(41.2)	(105.0)	(98.7)
Recovery of amounts previously written off	17.7	14.2	29.1	29.8
Balance at end of period	178.7	175.8	178.7	175.8
Change in allowance for credit losses			20.6	22.5
Uncollectible expense
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses deferred for future recovery or refund	(12.4)	(16.6)	23.2	4.3
Utility Operations
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period			199.3
Balance at end of period	178.7		178.7
Wisconsin | Utility Operations
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	90.9	85.7	82.0	84.0
Provision for credit losses	6.7	11.8	17.9	23.6
Write-offs charged against the allowance	(29.1)	(22.1)	(58.0)	(50.9)
Recovery of amounts previously written off	11.8	8.0	18.0	17.9
Balance at end of period	76.4	78.0	76.4	78.0
Wisconsin | Utility Operations | Uncollectible expense
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses deferred for future recovery or refund	(3.9)	(5.4)	16.5	3.4
Illinois | Utility Operations
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	116.5	107.0	111.0	105.5
Provision for credit losses	4.8	7.1	13.3	18.4
Write-offs charged against the allowance	(21.3)	(17.9)	(44.3)	(45.2)
Recovery of amounts previously written off	5.5	6.0	10.3	11.4
Balance at end of period	97.0	91.0	97.0	91.0
Illinois | Utility Operations | Uncollectible expense
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses deferred for future recovery or refund	(8.5)	(11.2)	6.7	0.9
Other States | Utility Operations
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	6.4	7.9	6.3	8.8
Provision for credit losses	(0.4)	(0.1)	0.9	0.1
Write-offs charged against the allowance	(1.1)	(1.2)	(2.7)	(2.6)
Recovery of amounts previously written off	0.4	0.2	0.8	0.5
Balance at end of period	5.3	6.8	5.3	6.8
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