Document and Entity Information - shares	3 Months Ended
	Dec. 31, 2017	Jan. 29, 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		48,344,121
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
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		24,577
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
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		1,972,052
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2017