Financing -Schedule of Short-term Borrowings (Details) - USD ($) $ in Millions	6 Months Ended
Mar. 31, 2022	Sep. 30, 2021	Mar. 31, 2021
Spire Alabama \| Spire Note
Short-term Debt [Line Items]
Highest borrowings outstanding	$ 191.6
Lowest borrowings outstanding	38.4
Weighted average borrowings	$ 116.8
Weighted average interest rate	0.40%
Borrowings outstanding	$ 156.6	$ 49.0
Weighted average interest rate	0.90%	0.20%
Spire Missouri
Short-term Debt [Line Items]
Highest borrowings outstanding	$ 250.0
Weighted average borrowings	$ 226.6
Weighted average interest rate	0.80%
Borrowings outstanding		$ 250.0	$ 250.0
Weighted average interest rate		0.70%	0.80%
Spire Missouri \| Spire Note
Short-term Debt [Line Items]
Highest borrowings outstanding	$ 412.0
Lowest borrowings outstanding	43.2
Weighted average borrowings	$ 220.0
Weighted average interest rate	0.30%
Borrowings outstanding	$ 277.2	$ 240.9	$ 369.4
Weighted average interest rate	0.90%	0.20%	0.20%
Spire
Short-term Debt [Line Items]
Highest borrowings outstanding	$ 996.8
Lowest borrowings outstanding	556.0
Weighted average borrowings	$ 799.1
Weighted average interest rate	0.50%
Borrowings outstanding	$ 607.1	$ 672.0	$ 653.5
Weighted average interest rate	0.90%	0.40%	0.40%
Spire \| Commercial Paper Notes
Short-term Debt [Line Items]
Highest borrowings outstanding	$ 746.8
Lowest borrowings outstanding	408.0
Weighted average borrowings	$ 572.5
Weighted average interest rate	0.40%
Borrowings outstanding	$ 607.1	$ 422.0	$ 403.5
Weighted average interest rate	0.90%	0.20%	0.20%

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

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- Definition

The average effective interest rate during the reporting period.

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Average amount borrowed under the credit facility 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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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.

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No definition available.

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