Document and Entity Information - shares	9 Months Ended
	Jun. 30, 2018	Jul. 30, 2018
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 Common Stock, Shares Outstanding (in shares)		50,669,092
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Spire Missouri
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 Common Stock, Shares Outstanding (in shares)		24,577
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Spire Alabama
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 Common Stock, Shares Outstanding (in shares)		1,972,052
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018