| Document and Entity Information | Jul. 01, 2020 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jul. 1, 2020 |
| Entity Registrant Name | Spire Inc. |
| Entity Central Index Key | 0001126956 |
| Entity Emerging Growth Company | false |
| Entity File Number | 1-16681 |
| Entity Incorporation, State or Country Code | MO |
| Entity Tax Identification Number | 74-2976504 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Common Stock $1.00 par value | |
| Document Information [Line Items] | |
| Security12b Title | Common Stock $1.00 par value |
| Trading Symbol | SR |
| Security Exchange Name | NYSE |
| Depositary Shares, each representing a 1/1,000th interest in a share of 5.90% Series A Cumulative Redeemable Perpetual Preferred Stock, par value | |
| Document Information [Line Items] | |
| Security12b Title | Depositary Shares |
| Trading Symbol | SR.PRA |
| Security Exchange Name | NYSE |
