v3.26.1
Divestitures - Schedule of Information Related to Discontinued Operations Assets and Liabilities (Details) - USD ($)
$ in Millions
Jun. 30, 2026
Sep. 30, 2025
Jun. 30, 2025
Disposal Group, Including Discontinued Operations [Line Items]      
Non-current assets held for sale $ 0.0 $ 445.9 $ 446.1
Current assets held for sale 81.4 182.7 199.9
Current liabilities held for sale 7.9 124.2 132.4
Non-current liabilities held for sale 0.0 $ 7.4 7.1
Discontinued Operations, Held-for-Sale [Member]      
Disposal Group, Including Discontinued Operations [Line Items]      
Non-utility property (net of accum. depreciation and amortization) 442.5   442.3
Other non-current assets 3.4   3.8
Non-current assets held for sale 445.9   446.1
Accounts receivable, net 105.3   117.6
Inventory 34.2   36.9
Prepayments 1.7   2.0
Derivative instrument assets 41.5   43.4
Current assets held for sale 182.7   199.9
Accounts payable 92.0   100.0
Wages and compensation accrued 4.9   4.3
Taxes accrued 1.5   1.1
Other 25.8   27.0
Current liabilities held for sale 124.2   132.4
Asset retirement obligations 5.6   5.5
Deferred Credits and Other Liabilities held for sale 1.8   1.6
Non-current liabilities held for sale 7.4   7.1
Discontinued Operations, Held-for-Sale [Member] | Spire Marketing [Member]      
Disposal Group, Including Discontinued Operations [Line Items]      
Non-utility property (net of accum. depreciation and amortization) 1.0   1.1
Other non-current assets 2.0   2.4
Non-current assets held for sale 3.0   3.5
Accounts receivable, net 93.3   109.6
Inventory 31.8   30.5
Prepayments 0.2   0.2
Derivative instrument assets 41.5   43.5
Current assets held for sale 166.8   183.8
Accounts payable 85.6   92.0
Wages and compensation accrued 4.0   3.7
Taxes accrued 0.5   0.4
Other 16.7   15.8
Current liabilities held for sale 106.8   111.9
Asset retirement obligations 0.0   0.0
Deferred Credits and Other Liabilities held for sale 1.6   1.4
Non-current liabilities held for sale 1.6   1.4
Discontinued Operations, Held-for-Sale [Member] | Spire Storage [Member]      
Disposal Group, Including Discontinued Operations [Line Items]      
Non-utility property (net of accum. depreciation and amortization) 441.5   441.2
Other non-current assets 1.4   1.4
Non-current assets held for sale 442.9   442.6
Accounts receivable, net 12.0   8.0
Inventory 2.4   6.4
Prepayments 1.5   1.8
Derivative instrument assets 0.0   (0.1)
Current assets held for sale 15.9   16.1
Accounts payable 6.4   8.0
Wages and compensation accrued 0.9   0.6
Taxes accrued 1.0   0.7
Other 9.1   11.2
Current liabilities held for sale 17.4   20.5
Asset retirement obligations 5.6   5.5
Deferred Credits and Other Liabilities held for sale 0.2   0.2
Non-current liabilities held for sale 5.8   $ 5.7
Discontinued Operations, Held-for-Sale [Member] | Spire Mississippi [Member]      
Disposal Group, Including Discontinued Operations [Line Items]      
Utility Plant 95.1    
Less - Accumulated depreciation and amortization (32.5)    
Net Utility Plant 62.6    
Accounts receivable, net 2.9    
Materials and supplies 0.8    
Regulatory Assets 0.9    
Goodwill 14.2    
Current assets held for sale 81.4    
Accounts payable 1.0    
Regulatory liabilities - Current 0.0    
Asset retirement obligations 3.2    
Regulatory liabilities 1.4    
Other 2.3    
Current liabilities held for sale $ 7.9