v3.26.1
Acquisitions - Summary of Preliminary Purchase Price Allocation and Estimated Fair Values of Assets Acquired and Liabilities Assumed (Details) - USD ($)
$ in Millions
 6 Months Ended
Mar. 31, 2026
Mar. 31, 2026
Mar. 31, 2025
Sep. 30, 2025
Business Combination [Line Items]        
Acquisition consideration:   $ 2,500.8 $ 0.0  
Liabilities assumed:        
Goodwill $ 1,891.4 1,891.4 $ 1,171.6 $ 1,171.6
Piedmont Tennessee Transaction [Member]        
Business Combination [Line Items]        
Acquisition consideration: 2,500.8      
Assets acquired:        
Utility plant 1,829.4 1,829.4    
Accounts receivable (net allowance of $1.7) 65.2 65.2    
Inventories 7.1 7.1    
Current regulatory assets 33.4 33.4    
Other current assets 35.6 35.6    
Non-current regulatory assets 42.1 42.1    
Other non-current assets 0.4 0.4    
Total assets acquired 2,013.2 2,013.2    
Liabilities assumed:        
Accounts payable 33.5 33.5    
Other current liabilities 31.8 31.8    
Non-current regulatory liabilities 173.5 173.5    
Other non-current liabilities 11.5 11.5    
Total liabilities assumed 250.3 250.3    
Net assets acquired 1,762.9 1,762.9    
Goodwill $ 737.9 $ 737.9