v3.26.1
Segment Information - Schedule of Financial Data Related to Gross Receipt Taxes and Capital Expenditures (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Property, Plant, and Equipment [Line Items]        
Capital Expenditures     $ 608.4 $ 699.7
Spire Missouri [Member]        
Property, Plant, and Equipment [Line Items]        
Gross Receipt Taxes $ 14.5 $ 13.9 78.3 73.3
Capital Expenditures 152.5 159.8 435.7 481.9
Spire Alabama Inc [Member]        
Property, Plant, and Equipment [Line Items]        
Gross Receipt Taxes 5.0 5.0 24.3 24.1
Capital Expenditures $ 38.4 $ 39.7 $ 124.8 $ 102.8