Financing - Schedule of Short-term Borrowings (Details) - USD ($) $ in Millions	3 Months Ended
Dec. 31, 2024	Sep. 30, 2024	Dec. 31, 2023
Short-Term Debt [Line Items]
Highest borrowings outstanding	$ 1,198.0
Lowest borrowings outstanding	943.5
Weighted average borrowings	$ 1,087.8
Weighted average interest rate	4.60%
Borrowings outstanding	$ 1,158.0	$ 947.0	$ 1,047.5
Weighted average interest rate	4.40%	5.20%	5.70%
Term Loan [Member] \| Spire Missouri [Member]
Short-Term Debt [Line Items]
Highest borrowings outstanding	$ 0.0
Lowest borrowings outstanding	0.0
Weighted average borrowings	$ 0.0
Weighted average interest rate	0.00%
Borrowings outstanding	$ 0.0	$ 0.0	$ 0.0
Weighted average interest rate	0.00%	0.00%	0.00%
Spire Note [Member] \| Spire Missouri [Member]
Short-Term Debt [Line Items]
Highest borrowings outstanding	$ 599.0
Lowest borrowings outstanding	487.8
Weighted average borrowings	$ 545.3
Weighted average interest rate	4.90%
Borrowings outstanding	$ 580.9	$ 495.3	$ 633.3
Weighted average interest rate	4.80%	5.20%	5.70%
Spire Note [Member] \| Spire Alabama Inc [Member]
Short-Term Debt [Line Items]
Highest borrowings outstanding	$ 73.2
Lowest borrowings outstanding	43.0
Weighted average borrowings	$ 58.0
Weighted average interest rate	4.90%
Borrowings outstanding	$ 67.0	$ 48.4	$ 128.5
Weighted average interest rate	4.80%	5.20%	5.70%
Parent Company [Member] \| Commercial Paper [Member]
Short-Term Debt [Line Items]
Highest borrowings outstanding	$ 1,198.0
Lowest borrowings outstanding	943.5
Weighted average borrowings	$ 1,087.8
Weighted average interest rate	4.60%
Borrowings outstanding	$ 1,158.0	$ 947.0	$ 1,047.5
Weighted average interest rate	4.40%	5.20%	5.70%

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

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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.

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- 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.

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

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

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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.

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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.

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