Note 6 - Financing - Short-term Borrowings (Details) - USD ($) $ in Millions	6 Months Ended
Mar. 31, 2024	Sep. 30, 2023	Mar. 31, 2023
Highest borrowings outstanding	$ 1,275.0
Lowest borrowings outstanding	754.6
Weighted average borrowings	$ 1,027.9
Weighted average interest rate	5.80%
Borrowings outstanding	$ 786.0	$ 955.5	$ 561.0
Weighted average interest rate	5.80%	5.60%	5.40%
Spire Alabama Inc [Member] \| Spire Note [Member]
Highest borrowings outstanding	$ 132.5
Lowest borrowings outstanding	25.2
Weighted average borrowings	$ 94.5
Weighted average interest rate	5.70%
Borrowings outstanding	$ 37.4	$ 124.1	$ 121.3
Weighted average interest rate	5.60%	5.60%	5.30%
Spire Note [Member] \| Spire Missouri [Member]
Highest borrowings outstanding	$ 643.6
Lowest borrowings outstanding	234.7
Weighted average borrowings	$ 469.9
Weighted average interest rate	5.70%
Borrowings outstanding	$ 243.9	$ 540.6	$ 60.7
Weighted average interest rate	5.60%	5.60%	5.30%
Parent Company [Member] \| Commercial Paper [Member]
Highest borrowings outstanding	$ 1,135.0
Lowest borrowings outstanding	554.6
Weighted average borrowings	$ 930.6
Weighted average interest rate	5.70%
Borrowings outstanding	$ 586.0	$ 955.5	$ 361.0
Weighted average interest rate	5.60%	5.60%	5.30%

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

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

+ References

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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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