v3.26.3
Reportable Segments (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Apr. 30, 2026
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Segment Reporting [Line Items]            
Revenue from external customers   $ 613.6 $ 540.9 $ 1,809.0 $ 1,693.5  
Costs associated with service revenues   8.2 8.4 32.5 23.6  
Costs associated with product sales   152.0 101.9 363.9 320.4  
Operation and maintenance   86.1 79.7 221.4 212.9  
Administrative and general   62.4 50.4 180.6 145.2  
Taxes other than income taxes   35.8 32.6 105.8 98.2  
Loss (gain) on sale of assets, impairments and other   8.8 0.2 8.5 (0.7)  
Miscellaneous other income, net   1.8 1.0 6.2 2.8  
Segment EBITDA   262.1 268.7 902.5 896.7  
Depreciation and amortization   112.4 106.2 333.8 330.6  
Interest expense   34.9 39.5 113.9 118.8  
Interest income   (0.9) (4.0) (7.7) (8.0)  
Consolidated income before income taxes   115.7 127.0 462.5 455.3  
Total Assets   10,459.0   10,459.0   $ 10,513.4
Capital expenditures       550.2 222.4  
Payments to acquire businesses, net of cash acquired       205.7 0.0  
Spire Marketing, Inc. | Boardwalk Pipelines, LP            
Segment Reporting [Line Items]            
Payments to acquire businesses, net of cash acquired $ 205.7     205.7    
Operating Segments            
Segment Reporting [Line Items]            
Revenue from external customers   613.6 540.9 1,809.0 1,693.5  
Total Assets   9,463.3   9,463.3   9,075.0
Natural Gas Reportable Segment            
Segment Reporting [Line Items]            
Revenue from external customers   417.1 358.7 1,246.1 1,131.8  
Natural Gas Reportable Segment | Operating Segments            
Segment Reporting [Line Items]            
Revenue from external customers   417.1 358.7 1,246.1 1,131.8  
Costs associated with service revenues   1.9 3.2 16.4 9.8  
Costs associated with product sales   37.7 0.0 52.0 0.0  
Operation and maintenance   72.3 67.8 183.2 178.4  
Administrative and general   55.1 42.6 159.8 124.1  
Taxes other than income taxes   32.5 29.4 96.3 88.6  
Loss (gain) on sale of assets, impairments and other   8.7 0.2 8.4 (0.7)  
Miscellaneous other income, net   (1.8) (1.0) (6.1) (2.8)  
Segment EBITDA   210.7 216.5 736.1 734.4  
Total Assets   8,014.4   8,014.4   7,591.2
Capital expenditures       520.2 198.7  
Natural Gas Liquids Reportable Segment            
Segment Reporting [Line Items]            
Revenue from external customers   196.5 182.2 562.9 561.7  
Natural Gas Liquids Reportable Segment | Operating Segments            
Segment Reporting [Line Items]            
Revenue from external customers   196.5 182.2 562.9 561.7  
Costs associated with service revenues   6.3 5.2 16.1 13.8  
Costs associated with product sales   114.3 101.9 311.9 320.4  
Operation and maintenance   13.8 11.9 38.2 34.5  
Administrative and general   7.3 7.8 20.8 21.1  
Taxes other than income taxes   3.3 3.2 9.5 9.6  
Loss (gain) on sale of assets, impairments and other   0.1 0.0 0.1 0.0  
Miscellaneous other income, net   0.0 0.0 (0.1) 0.0  
Segment EBITDA   51.4 $ 52.2 166.4 162.3  
Total Assets   $ 1,448.9   1,448.9   $ 1,483.8
Capital expenditures       $ 30.0 $ 23.7