Document and Entity Information - shares	3 Months Ended
	Dec. 31, 2018	Feb. 04, 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)		50,740,277
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	SR
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
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 Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	SR
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
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 Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	SR
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2018