Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions |
1 Months Ended | 6 Months Ended | |
|---|---|---|---|
Apr. 30, 2026 |
Aug. 31, 2024 |
Mar. 31, 2026 |
|
| Long-Term Purchase Commitment [Line Items] | |||
| Long-term purchase commitment, amount | $ 1,762.9 | ||
| Capital committed to contribute to partnership | 25.0 | ||
| Remaining unfunded capital commitment | 15.0 | ||
| Spire Missouri [Member] | |||
| Long-Term Purchase Commitment [Line Items] | |||
| Long-term purchase commitment, amount | 1,295.0 | ||
| Spire Alabama Inc [Member] | |||
| Long-Term Purchase Commitment [Line Items] | |||
| Long-term purchase commitment, amount | $ 553.1 | ||
| Piedmont Natural Gas Co | |||
| Long-Term Purchase Commitment [Line Items] | |||
| Court jury awarded a verdict , value | $ 18.6 | ||
| Piedmont Natural Gas Co | Subsequent Event [Member] | |||
| Long-Term Purchase Commitment [Line Items] | |||
| Loss Contingency Interest Accrual | $ 3.2 | ||