| Document And Entity Information | Sep. 30, 2023 |
| Document Information [Line Items] | |
| Entity, Registrant Name | Spire Inc. |
| Document, Type | 8-K |
| Document, Period End Date | Nov. 16, 2023 |
| Entity, File Number | 1-16681 |
| Entity, Address, Address Line One | 700 Market Street |
| Entity, Address, City or Town | St. Louis |
| Entity, Address, State or Province | MO |
| Entity, Address, Postal Zip Code | 63101 |
| City Area Code | 314 |
| Local Phone Number | 342-0500 |
| Entity, Incorporation, State or Country Code | MO |
| Entity, Tax Identification Number | 74-2976504 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity, Emerging Growth Company | false |
| Amendment Flag | false |
| Entity, Central Index Key | 0001126956 |
| CommonStock100ParValue Custom [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common Stock $1.00 par value |
| Trading Symbol | SR |
| Security Exchange Name | NYSE |
| DepositaryShares Custom [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Depositary Shares |
| Trading Symbol | SR.PRA |
| Security Exchange Name | NYSE |
