Document and Entity Information - USD ($)
12 Months Ended
Sep. 30, 2019
Nov. 21, 2019
Mar. 31, 2019
Entity Information [Line Items]   
Entity Registrant NameSpire Inc  
Entity Central Index Key0001126956  
Current Fiscal Year End Date--09-30  
Entity Well-known Seasoned IssuerYes  
Entity Voluntary FilersNo  
Entity Current Reporting StatusYes  
Entity Filer CategoryLarge Accelerated Filer  
Entity Public Float  $ 4,053,711,051
Entity Emerging Growth Companyfalse  
Entity Small Businessfalse  
Entity Shell Companyfalse  
Entity Common Stock, Shares Outstanding (in shares) 50,977,062 
Document Period End DateSep. 30, 2019  
Document Fiscal Year Focus2019  
Document Fiscal Period FocusFY  
Document Type10-K  
Amendment Flagfalse  
Entity File Number1-16681  
Entity Tax Identification Number74-2976504  
Entity Address, Address Line One700 Market Street  
Entity Address, City or TownSt. Louis  
Entity Address, State or ProvinceMO  
Entity Address, Postal Zip Code63101  
City Area Code314  
Local Phone Number342-0500  
Entity Incorporation, State or Country CodeMO  
Document Annual Reporttrue  
Document Transition Reportfalse  
Entity Interactive Data CurrentYes  
Documents Incorporated by ReferencePortions 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 SymbolSR  
Title of each classCommon Stock $1.00 par value  
Name of each exchange on which registeredNYSE  
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 SymbolSR.PRA  
Title of each classDepositary Shares  
Name of each exchange on which registeredNYSE  
Spire Missouri Inc   
Entity Information [Line Items]   
Entity Registrant NameSpire Missouri Inc  
Entity Central Index Key0000057183  
Current Fiscal Year End Date--09-30  
Entity Well-known Seasoned IssuerNo  
Entity Voluntary FilersNo  
Entity Current Reporting StatusYes  
Entity Filer CategoryNon-accelerated Filer  
Entity Public Float  0
Entity Emerging Growth Companyfalse  
Entity Small Businessfalse  
Entity Shell Companyfalse  
Entity Common Stock, Shares Outstanding (in shares) 24,577 
Document Period End DateSep. 30, 2019  
Document Fiscal Year Focus2019  
Document Fiscal Period FocusFY  
Document Type10-K  
Amendment Flagfalse  
Entity File Number1-1822  
Entity Tax Identification Number43-0368139  
Entity Address, Address Line One700 Market Street  
Entity Address, City or TownSt. Louis  
Entity Address, State or ProvinceMO  
Entity Address, Postal Zip Code63101  
City Area Code314  
Local Phone Number342-0500  
Entity Incorporation, State or Country CodeMO  
Entity Interactive Data CurrentYes  
Spire Alabama Inc   
Entity Information [Line Items]   
Entity Registrant NameSpire Alabama Inc  
Entity Central Index Key0000003146  
Current Fiscal Year End Date--09-30  
Entity Well-known Seasoned IssuerNo  
Entity Voluntary FilersNo  
Entity Current Reporting StatusYes  
Entity Filer CategoryNon-accelerated Filer  
Entity Public Float  $ 0
Entity Emerging Growth Companyfalse  
Entity Small Businessfalse  
Entity Shell Companyfalse  
Entity Common Stock, Shares Outstanding (in shares) 1,972,052 
Document Period End DateSep. 30, 2019  
Document Fiscal Year Focus2019  
Document Fiscal Period FocusFY  
Document Type10-K  
Amendment Flagfalse  
Entity File Number2-38960  
Entity Tax Identification Number63-0022000  
Entity Address, Address Line One2101 6th Avenue North  
Entity Address, City or TownBirmingham  
Entity Address, State or ProvinceAL  
Entity Address, Postal Zip Code35203  
City Area Code205  
Local Phone Number326-8100  
Entity Incorporation, State or Country CodeAL  
Entity Interactive Data CurrentYes  

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