The number of manufactured gas plant (MGP) sites in Missouri posing potential environmental liability at St Louis.

No definition available.

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Namespace Prefix:	lg_
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- Definition

The number of manufactured gas plant (MGP) sites in Missouri posing potential environmental liability at Shrewsbury.

+ References

No definition available.

+ Details

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Namespace Prefix:	lg_
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- Definition

Number Of Incident Fatalities

+ References

No definition available.

+ Details

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Namespace Prefix:	lg_
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Balance Type:	na
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- Definition

Site Contingency, Number of Former Manufactured Gas Distribution

+ References

No definition available.

+ Details

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Namespace Prefix:	lg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Site Contingency, Number of Former Manufactured Gas Plant

+ References

No definition available.

+ Details

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Namespace Prefix:	lg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of claims settled.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The total number of new claims filed pertaining to a loss contingency during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of plaintiffs that have filed claims pertaining to a loss contingency.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of pending claims pertaining to a loss contingency.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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- Details

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Namespace Prefix:
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- Details

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Period Type:

- Details

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- Details

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Namespace Prefix:
Data Type:	na
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- Details

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- Details

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- Details

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COMMITMENTS AND CONTINGENCIES - Contingencies (Details)		12 Months Ended	54 Months Ended
COMMITMENTS AND CONTINGENCIES - Contingencies (Details)	Dec. 17, 2013 fatality	Sep. 30, 2017 plaintiff site lawsuit	Sep. 30, 2016 lawsuit	Sep. 30, 2015 site
Site Contingency [Line Items]
Number of incident fatalities \| fatality	1
Spire Missouri
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP) sites in Shrewsbury, Missouri		1
Number of former manufactured gas plant (MGP) sites in the City of St. Louis		2
Spire Missouri \| Previous Ownership
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP)				19
Missouri Gas Energy (MGE) \| Previous Ownership
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP)		7
Spire Alabama
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP)		9
Number of former manufactured gas distribution		5
Spire Alabama \| Current Ownership
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP)		4
Number of former manufactured gas distribution		1
Mobile Gas
Site Contingency [Line Items]
Number of lawsuits \| lawsuit			14
Number of lawsuits settled \| lawsuit			11
Number of lawsuits pending \| lawsuit		3
Mobile Gas \| Pending Litigation
Site Contingency [Line Items]
Number of plaintiffs \| plaintiff		270
Mobile Gas \| Previous Ownership
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP)				1