v3.26.1
Divestitures - Schedule of Assets and Liabilities Associated with Assets Held for Sale (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Sep. 30, 2025
Mar. 31, 2025
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Non-current assets held for sale $ 0.0 $ 445.9 $ 439.2
Current assets held for sale 725.3 182.7 200.9
Current liabilities held for sale 134.7 124.2 179.3
Non-current liabilities held for sale 0.0 7.4 7.9
Discontinued Operations, Held-for-Sale [Member]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Non-utility property (net of accum. depreciation and amortization) 444.8    
Non-utility property (net of accum. depreciation and amortization)   442.5 435.5
Other investments 0.3    
Other Investments   3.4 3.7
Non-current assets held for sale   445.9 439.2
Accounts receivable, net 93.7 105.3 138.2
Inventory 15.5 34.2 14.1
Prepayments 1.9 1.7 2.7
Derivative instrument assets 85.1 41.5 45.9
Other 1.3    
Current assets held for sale 642.6 182.7 200.9
Accounts payable 73.3 92.0 122.4
Wages and compensation accrued 4.1 4.9 4.1
Taxes accrued 1.5    
Deferred income taxes   1.5 0.7
Asset retirement obligations 5.7    
Other 39.3 25.8 52.1
Current liabilities held for sale 123.9 124.2 179.3
Asset retirement obligations   5.6 5.5
Deferred Credits and Other Liabilities held for sale   1.8 2.4
Non-current liabilities held for sale   7.4 7.9
Discontinued Operations, Held-for-Sale [Member] | Spire Marketing [Member]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Non-utility property (net of accum. depreciation and amortization) 0.8    
Non-utility property (net of accum. depreciation and amortization)   1.0 1.6
Other investments 0.0    
Other Investments   2.0 2.4
Non-current assets held for sale   3.0 4.0
Accounts receivable, net 85.7 93.3 131.3
Inventory 13.0 31.8 9.1
Prepayments 0.8 0.2 0.5
Derivative instrument assets 85.1 41.5 45.8
Other 1.3    
Current assets held for sale 186.7 166.8 186.7
Accounts payable 70.7 85.6 111.1
Wages and compensation accrued 3.6 4.0 3.4
Taxes accrued 0.2    
Deferred income taxes   0.5 0.2
Asset retirement obligations 0.0    
Other 28.8 16.7 38.0
Current liabilities held for sale 103.3 106.8 152.7
Asset retirement obligations   0.0 0.0
Deferred Credits and Other Liabilities held for sale   1.6 2.2
Non-current liabilities held for sale   1.6 2.2
Discontinued Operations, Held-for-Sale [Member] | Spire Storage [Member]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Non-utility property (net of accum. depreciation and amortization) 444.0    
Non-utility property (net of accum. depreciation and amortization)   441.5 433.9
Other investments 0.3    
Other Investments   1.4 1.3
Non-current assets held for sale   442.9 435.2
Accounts receivable, net 8.0 12.0 6.9
Inventory 2.5 2.4 5.0
Prepayments 1.1 1.5 2.2
Derivative instrument assets 0.0 (0.0) 0.1
Other 0.0    
Current assets held for sale 455.9 15.9 14.2
Accounts payable 2.6 6.4 11.3
Wages and compensation accrued 0.5 0.9 0.7
Taxes accrued 1.3    
Deferred income taxes   1.0 0.5
Asset retirement obligations 5.7    
Other 10.5 9.1 14.1
Current liabilities held for sale 20.6 17.4 26.6
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]      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Utility Plant 94.9    
Less - Accumulated depreciation and amortization (32.5)    
Net Utility Plant 62.4    
Accounts receivable, net 4.6    
Materials and supplies 0.7    
Regulatory Assets 0.8    
Goodwill 14.2    
Current assets held for sale 82.7    
Accounts payable 1.4    
Regulatory liabilities - Current 0.1    
Asset retirement obligations 3.2    
Regulatory liabilities 1.4    
Other 4.7    
Current liabilities held for sale $ 10.8