v3.26.1
Segment Information - Schedule of Information about Segment Revenue, Segment Expenses, and Net Income (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Segment Reporting Information [Line Items]        
Gas utility operating revenues $ 420.2 $ 352.5 $ 2,138.9 $ 1,946.9
Depreciation and amortization expense 95.2 72.8 257.4 216.1
Interest expense 85.6 47.9 206.2 139.4
Income tax (benefit) expense (15.3) (7.9) 58.8 55.6
Net Income From Discontinued Operations, Net of Tax 253.8 34.2 325.6 63.4
Net Income 211.2 20.9 588.4 311.5
Operating Segments [Member] | Gas Utility [Member]        
Segment Reporting Information [Line Items]        
Gas utility operating revenues 416.1 347.5 2,124.3 1,931.2
Cost of gas sold, incl. gross receipts taxes 131.4 124.5 904.7 891.7
Operation and maintenance expense 134.8 114.1 376.5 351.9
Depreciation and amortization expense 92.3 70.0 248.7 207.6
Interest expense 44.6 33.2 116.7 102.1
Income tax (benefit) expense (3.4) (3.0) 77.1 58.3
Other segment items [1] 31.6 23.7 90.6 72.3
Other net loss [2] (31.5) (3.3) (61.8) (14.9)
Net Income From Discontinued Operations, Net of Tax 253.8 34.2 325.6 63.4
Net Income 211.2 20.9 588.4 311.5
Capital expenditures 206.0 213.0 590.6 608.1
Intersegment Eliminations [Member]        
Segment Reporting Information [Line Items]        
Gas utility operating revenues [3] $ 4.1 $ 5.0 $ 14.6 $ 15.7
[1] Other segment items include taxes other than income excluding gross receipt tax, miscellaneous income and deductions, and other revenue eliminations.
[2] Other net loss of the Company's consolidated information include Spire's subsidiaries engaged in the transportation of natural gas, risk management, among other activities, and unallocated corporate items, including transition and transaction cost associated with the Tennessee Transaction and financing costs.
[3] Includes other operating revenues net of elimination of Spire subsidiaries noted in (b) above.