Note 13 - Pension Plans and Other Postretirement Benefits - Assumption Used (Details)	12 Months Ended
Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Pension 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	6.75%	6.75%	7.25%
Weighted average discount rate		3.10%	2.95%
Spire Alabama Inc [Member] \| Pension Plan [Member] \| Maximum [Member]
Weighted average discount rate	3.10%	2.95%	3.25%
Weighted average discount rate	5.70%	3.10%
Spire Alabama Inc [Member] \| Pension Plan [Member] \| Minimum [Member]
Weighted average discount rate	3.00%	2.80%	3.20%
Weighted average discount rate	5.65%	3.00%
Spire Alabama Inc [Member] \| Other Postretirement Benefits Plan [Member]
Weighted average discount rate	2.95%	2.75%	3.15%
Weighted average discount rate	5.80%	2.95%
Spire Alabama Inc [Member] \| Other Postretirement Benefits Plan [Member] \| Maximum [Member]
Expected long-term rate of return on plan assets	6.25%	6.25%	6.25%
Spire Alabama Inc [Member] \| Other Postretirement Benefits Plan [Member] \| Minimum [Member]
Expected long-term rate of return on plan assets	5.00%	5.00%	5.00%
Spire Missouri East [Member] \| Pension Plan [Member]
Weighted average discount rate	3.00%	2.85%	3.20%
Weighted average discount rate	5.70%	3.00%
Spire Missouri East [Member] \| Other Postretirement Benefits Plan [Member]
Weighted average rate of future compensation increase	3.00%	3.00%
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	6.75%	6.75%	7.25%
Weighted average discount rate		3.00%	2.85%
Spire Missouri [Member] \| Other Postretirement Benefits Plan [Member]
Weighted average discount rate	2.95%	2.75%	3.15%
Weighted average rate of future compensation increase	3.00%	3.00%	3.00%
Expected long-term rate of return on plan assets	5.75%	5.75%	6.25%
Weighted average discount rate	5.80%	2.95%
Spire Missouri West [Member] \| Pension Plan [Member]
Weighted average discount rate	3.00%	2.75%	3.15%
Weighted average discount rate	5.80%	3.00%
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.

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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

+ Details

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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

+ Details

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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

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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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 8
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e2919-114920

+ Details

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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

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- Details

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Namespace Prefix:
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- Details

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- Details

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- Details

Name:	srt_RangeAxis=srt_MinimumMember
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Data Type:	na
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- Details

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Data Type:	na
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- Details

Name:	dei_LegalEntityAxis=sr_SpireMissouriEastMember
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Data Type:	na
Balance Type:
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- Details

Name:	dei_LegalEntityAxis=sr_SpireMissouriMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	dei_LegalEntityAxis=sr_SpireMissouriWestMember
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Data Type:	na
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- Details

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