v3.26.3
CREDIT LOSSES - ROLLFORWARD OF ALLOWANCES (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Accounts Receivable, Allowance for Credit Loss [Roll Forward]        
Balance at beginning of period $ 148.9 $ 142.2 $ 148.7 $ 162.8
Provision for credit losses 64.2 32.8 193.1 100.8
Write-offs charged against the allowance (50.2) (52.9) (170.0) (167.8)
Recoveries of amounts previously written off 18.8 33.5 60.7 87.1
Balance at end of period 139.9 129.5 139.9 129.5
Change in allowance for credit losses     (8.8) (33.3)
Uncollectible expense        
Accounts Receivable, Allowance for Credit Loss [Roll Forward]        
Provision for credit losses deferred for future recovery or refund (41.8) (26.1) (92.6) (53.4)
Public Utilities        
Accounts Receivable, Allowance for Credit Loss [Roll Forward]        
Balance at beginning of period     148.7  
Balance at end of period 139.9   139.9  
Wisconsin | Public Utilities        
Accounts Receivable, Allowance for Credit Loss [Roll Forward]        
Balance at beginning of period 61.2 52.3 61.7 73.6
Provision for credit losses 51.5 21.8 150.8 59.6
Write-offs charged against the allowance (36.1) (35.7) (112.0) (108.0)
Recoveries of amounts previously written off 12.2 11.3 39.4 37.5
Balance at end of period 55.2 48.7 55.2 48.7
Wisconsin | Public Utilities | Uncollectible expense        
Accounts Receivable, Allowance for Credit Loss [Roll Forward]        
Provision for credit losses deferred for future recovery or refund (33.6) (1.0) (84.7) (14.0)
Illinois | Public Utilities        
Accounts Receivable, Allowance for Credit Loss [Roll Forward]        
Balance at beginning of period 83.7 84.6 82.3 83.9
Provision for credit losses 11.7 11.6 41.0 41.3
Write-offs charged against the allowance (12.9) (12.2) (55.0) (53.5)
Recoveries of amounts previously written off 6.2 17.7 20.1 44.3
Balance at end of period 80.5 76.6 80.5 76.6
Illinois | Public Utilities | Uncollectible expense        
Accounts Receivable, Allowance for Credit Loss [Roll Forward]        
Provision for credit losses deferred for future recovery or refund (8.2) (25.1) (7.9) (39.4)
Other States | Public Utilities        
Accounts Receivable, Allowance for Credit Loss [Roll Forward]        
Balance at beginning of period 4.0 5.3 4.7 5.3
Provision for credit losses 1.0 (0.6) 1.3 (0.1)
Write-offs charged against the allowance (1.2) (5.0) (3.0) (6.3)
Recoveries of amounts previously written off 0.4 4.5 1.2 5.3
Balance at end of period 4.2 4.2 4.2 4.2
Other States | Public Utilities | 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