Note 7 - Notes Payable and Credit Agreements - Short-term Borrowings (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2023	Sep. 30, 2022
Term Loan [Member] \| Spire Missouri [Member]
Highest borrowings outstanding	$ 656.9
Lowest borrowings outstanding	3.8
Weighted average borrowings	$ 327.9
Weighted average interest rate	4.90%
Borrowings outstanding	$ 540.6	$ 445.3
Weighted average interest rate	5.60%
Spire Note [Member] \| Spire Missouri [Member]
Highest borrowings outstanding	$ 274.0
Lowest borrowings outstanding	76.7
Weighted average borrowings	$ 119.1
Weighted average interest rate	4.90%
Borrowings outstanding	$ 124.1	$ 260.9
Weighted average interest rate	5.60%	3.30%
Spire Note [Member] \| Spire Alabama Inc [Member]
Highest borrowings outstanding	$ 1,482.0
Lowest borrowings outstanding	489.0
Weighted average borrowings	$ 843.1
Weighted average interest rate	5.00%
Borrowings outstanding	$ 955.5	$ 1,037.5
Weighted average interest rate	5.60%	3.30%
Parent Company [Member] \| Term Loan [Member]
Highest borrowings outstanding	$ 250.0
Lowest borrowings outstanding	0.0
Weighted average borrowings	$ 66.8
Weighted average interest rate	5.50%
Borrowings outstanding	$ 0.0	$ 0.0
Weighted average interest rate		0.00%
Parent Company [Member] \| Commercial Paper [Member]
Highest borrowings outstanding	1,282.0
Lowest borrowings outstanding	354.4
Weighted average borrowings	$ 776.3
Weighted average interest rate	5.00%
Borrowings outstanding	$ 955.5	$ 1,037.5
Weighted average interest rate	5.60%	3.30%

Minimum amount borrowed under the credit facility at any time during the period.

No definition available.

Name:	sr_ShorttermDebtMinimumAmountOutstandingDuringPeriod
Namespace Prefix:	sr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 852
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481372/852-10-55-10

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16)(a)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19)(a))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Weighted average interest rate of short-term debt outstanding calculated at point in time.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

+ Details

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

- Definition

Weighted average interest rate of short-term debt outstanding calculated over time.

+ References

No definition available.

+ Details

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

- Definition

For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, average borrowings during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(3))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1402
-Paragraph (a)
-Publisher SEC

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1402
-Paragraph (b)
-Subparagraph (1)
-Publisher SEC

+ Details

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Balance Type:	credit
Period Type:	duration

- Definition

For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, the maximum amount borrowed at any time during the period.

+ References

No definition available.

+ Details

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- Details

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- Details

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- Details

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