Document and Entity Information - shares	9 Months Ended
	Jun. 30, 2019	Jul. 26, 2019
Entity Information [Line Items]
Entity Registrant Name	Spire Inc
Entity Central Index Key	0001126956
Current Fiscal Year End Date	--09-30
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding (in shares)		50,809,437
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Trading Symbol	SR
Document Type	10-Q
Amendment Flag	false
Entity Shell Company	false
Entity File Number	1-16681
Entity Tax Identification Number	742976504
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
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 Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding (in shares)		24,577
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Trading Symbol	SR
Document Type	10-Q
Amendment Flag	false
Entity Shell Company	false
Entity File Number	1-1822
Entity Tax Identification Number	430368139
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
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 Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding (in shares)		1,972,052
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Trading Symbol	SR
Document Type	10-Q
Amendment Flag	false
Entity Shell Company	false
Entity File Number	2-38960
Entity Tax Identification Number	630022000
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