v3.26.1
Revenue - Schedule of Gross Receipts Taxes Associated Revenue (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Disaggregation of Revenue [Line Items]        
Gross receipts tax amounts $ 20.9 $ 19.6 $ 107.3 $ 101.6
Spire Missouri [Member]        
Disaggregation of Revenue [Line Items]        
Gross receipts tax amounts 14.5 13.9 78.3 73.3
Spire Alabama Inc [Member]        
Disaggregation of Revenue [Line Items]        
Gross receipts tax amounts $ 5.0 $ 5.0 $ 24.3 $ 24.1