Document and Entity Information - USD ($)	12 Months Ended
	Sep. 30, 2019	Nov. 21, 2019	Mar. 31, 2019
Entity Information [Line Items]
Entity Registrant Name	Spire Inc
Entity Central Index Key	0001126956
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 4,053,711,051
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		50,977,062
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	false
Entity File Number	1-16681
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
Entity Incorporation, State or Country Code	MO
Document Annual Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Documents Incorporated by Reference	Portions of proxy statement for Spire Inc. to be filed on or about December 13, 2019 — Part III. Certain exhibits as indicated in Part IV.
Common Stock $1.00 par value
Entity Information [Line Items]
Trading Symbol	SR
Title of each class	Common Stock $1.00 par value
Name of each exchange on which registered	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 $25.00 per share
Entity Information [Line Items]
Trading Symbol	SR.PRA
Title of each class	Depositary Shares
Name of each exchange on which registered	NYSE
Spire Missouri Inc
Entity Information [Line Items]
Entity Registrant Name	Spire Missouri Inc
Entity Central Index Key	0000057183
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Public Float			0
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		24,577
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	false
Entity File Number	1-1822
Entity Tax Identification Number	43-0368139
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 Interactive Data Current	Yes
Spire Alabama Inc
Entity Information [Line Items]
Entity Registrant Name	Spire Alabama Inc
Entity Central Index Key	0000003146
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Public Float			$ 0
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		1,972,052
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	false
Entity File Number	2-38960
Entity Tax Identification Number	63-0022000
Entity Address, Address Line One	2101 6th Avenue North
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 Interactive Data Current	Yes