Note 13 - Pension Plans and Other Postretirement Benefits - Assumption Used (Details)	12 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Pension Plan [Member]
Weighted average rate of future compensation increase	3.00%	3.00%
Spire Missouri East [Member] \| Pension Plan [Member]
Weighted average discount rate	5.70%	3.00%	2.85%
Weighted average discount rate	6.25%	5.70%
Spire Missouri East [Member] \| Other Postretirement Benefits Plan [Member]
Weighted average rate of future compensation increase	3.00%	3.00%
Spire Alabama Inc [Member] \| Pension Plan [Member]
Weighted average rate of future compensation increase	3.00%	3.00%	3.00%
Expected long-term rate of return on plan assets	6.50%	6.75%	6.75%
Spire Alabama Inc [Member] \| Pension Plan [Member] \| Maximum [Member]
Weighted average discount rate	5.65%	3.10%	2.80%
Weighted average discount rate	6.20%	5.70%
Spire Alabama Inc [Member] \| Pension Plan [Member] \| Minimum [Member]
Weighted average discount rate	5.65%	3.10%	2.95%
Weighted average discount rate	6.25%	5.65%
Spire Alabama Inc [Member] \| Other Postretirement Benefits Plan [Member]
Weighted average discount rate	5.80%	2.95%	2.75%
Spire Alabama Inc [Member] \| Other Postretirement Benefits Plan [Member] \| Maximum [Member]
Expected long-term rate of return on plan assets	6.00%	6.25%	6.25%
Spire Alabama Inc [Member] \| Other Postretirement Benefits Plan [Member] \| Minimum [Member]
Expected long-term rate of return on plan assets	4.75%	5.00%	5.00%
Spire Missouri [Member]
Weighted average discount rate	6.30%	5.80%
Spire Missouri [Member] \| Pension Plan [Member]
Weighted average rate of future compensation increase	3.00%	3.00%	3.00%
Expected long-term rate of return on plan assets	6.50%	6.75%	6.75%
Weighted average discount rate			3.00%
Spire Missouri [Member] \| Other Postretirement Benefits Plan [Member]
Weighted average discount rate	5.80%	2.95%	2.75%
Weighted average rate of future compensation increase	3.00%	3.00%	3.00%
Expected long-term rate of return on plan assets	5.50%	5.75%	5.75%
Spire Alabama And Spire Missouri [Member] \| Other Postretirement Benefits Plan [Member]
Weighted average discount rate	6.30%	5.80%
Spire Missouri West [Member] \| Pension Plan [Member]
Weighted average discount rate	5.80%	3.00%	2.75%
Weighted average discount rate	6.30%	5.80%
Spire Alabama or Spire Missouri [Member] \| Pension Plan [Member]
Cash balance interest crediting rate - Spire Alabama / Spire Missouri	4.25%	4.25%

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (k)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted-average interest crediting rate used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, cash balance and other defined benefit plans with promised interest crediting rate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (k)(4)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationWeightedAverageInterestCreditingRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-8

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=sr_SpireMissouriEastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=sr_SpireAlabamaIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=sr_SpireMissouriMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=sr_SpireAlabamaAndSpireMissouriMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=sr_SpireMissouriWestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=sr_SpireAlabamaOrSpireMissouriMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: