v3.26.1
Divestitures - Additional Information (Details) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended 6 Months Ended 9 Months Ended
Apr. 21, 2026
Jun. 30, 2026
Apr. 30, 2026
Jun. 30, 2026
Mar. 31, 2026
Jun. 30, 2025
Mar. 31, 2026
Jun. 30, 2026
Jun. 30, 2025
Sep. 30, 2025
Disposal Group, Including Discontinued Operations [Line Items]                    
Cash proceeds from sale of business               $ 819.9 $ 0.0  
Goodwill   $ 1,895.2   $ 1,895.2   $ 1,171.6   1,895.2 1,171.6 $ 1,171.6
Impairment of property, plant and equipment       1.5   0.0   5.4 0.0  
Cash proceeds from sale         $ 30.0          
Pre-tax gain recognized         $ 28.9          
Spire Mississippi [Member]                    
Disposal Group, Including Discontinued Operations [Line Items]                    
Goodwill impairment             $ 3.9      
Discontinued Operations [Member]                    
Disposal Group, Including Discontinued Operations [Line Items]                    
Pretax gain on sale       (1.0)   45.1   93.8 83.6  
Income Tax Expense       (0.2)   10.9   22.8 20.2  
Discontinued Operations [Member] | Spire Marketing [Member]                    
Disposal Group, Including Discontinued Operations [Line Items]                    
Cash proceeds from sale of business     $ 212.0              
Pretax gain on sale     118.6 (5.1)   31.7   63.8 51.6  
Income Tax Expense     26.9 (1.3)   7.9   15.9 12.9  
Discontinued Operations , after-tax gain     $ 91.7              
Discontinued Operations [Member] | Spire Storage [Member]                    
Disposal Group, Including Discontinued Operations [Line Items]                    
Total expected consideration from transaction   657.0   657.0       657.0    
Cash proceeds from sale of business   607.0                
Pretax gain on sale   210.8   4.1   13.4   30.0 32.0  
Income Tax Expense   47.9   1.1   $ 3.0   6.9 $ 7.3  
Discontinued Operations , after-tax gain   162.9                
Deferred payment expected to be received in fiscal 2027   $ 50.0   50.0       50.0    
Discontinued Operations [Member] | Spire Mississippi [Member]                    
Disposal Group, Including Discontinued Operations [Line Items]                    
Goodwill impairment               $ 3.9    
Asset Held for Sale (Continuing Operations) [Member] | Spire Mississippi [Member]                    
Disposal Group, Including Discontinued Operations [Line Items]                    
Cash purchase price $ 75.0                  
Reverse termination fee 7.5                  
Goodwill 18.1                  
Goodwill impairment $ 3.9                  
Impairment of property, plant and equipment       $ 1.5