Document And Entity Information - shares	6 Months Ended
	Mar. 31, 2024	Apr. 28, 2024
Document Information [Line Items]
Entity Central Index Key	0001126956
Entity Registrant Name	Spire Inc.
Amendment Flag	false
Current Fiscal Year End Date	--09-30
Document Fiscal Period Focus	Q2
Document Fiscal Year Focus	2024
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
Document Transition Report	false
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
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		57,747,978
Spire Missouri [Member]
Document Information [Line Items]
Entity Central Index Key	0000057183
Entity Registrant Name	Spire Missouri Inc.
Amendment Flag	false
Current Fiscal Year End Date	--09-30
Document Fiscal Period Focus	Q2
Document Fiscal Year Focus	2024
Entity File Number	1-1822
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	43-0368139
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		25,855
Spire Alabama Inc [Member]
Document Information [Line Items]
Entity Central Index Key	0000003146
Entity Registrant Name	Spire Alabama Inc.
Amendment Flag	false
Current Fiscal Year End Date	--09-30
Document Fiscal Period Focus	Q2
Document Fiscal Year Focus	2024
Entity File Number	2-38960
Entity Address, Address Line One	605 Richard Arrington Blvd N
Entity Address, City or Town	Birmingham
Entity Address, State or Province	AL
Entity Address, Postal Zip Code	35203
City Area Code	205
Local Phone Number	326-8100
Entity Incorporation, State or Country Code	AL
Entity Tax Identification Number	63-0022000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		1,972,052
Depositary Shares [Member]
Document Information [Line Items]
Title of 12(b) Security	Depositary Shares
Trading Symbol	SR.PRA
Security Exchange Name	NYSE
Common Stock [Member]
Document Information [Line Items]
Title of 12(b) Security	Common Stock $1.00 par value
Trading Symbol	SR
Security Exchange Name	NYSE