Note 2 - Revenue - Disaggregated of Revenue (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
Feb. 28, 2021	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Operating Revenues		$ 2,198.5	$ 2,235.5	$ 1,855.4
Consolidation, Eliminations [Member]
Operating Revenues		(51.7)	(48.0)	(42.3)
Gas Utility [Member] \| Operating Segments [Member]
Operating Revenues		1,946.1	2,119.3	1,752.0
Gas Marketing [Member] \| Operating Segments [Member]
Operating Revenues		234.9	96.5	87.9
Other Segments [Member] \| Operating Segments [Member]
Operating Revenues		69.2	67.7	57.8
Spire [Member]
Operating Revenues		2,198.5	2,235.5	1,855.4
Spire [Member] \| Operating Segments [Member]
Operating Revenues		2,250.2	2,283.5	1,897.7
Spire [Member] \| Consolidation, Eliminations [Member]
Operating Revenues		(51.7)		(42.3)
Spire [Member] \| Segment Reconciling Items [Member]
Operating Revenues			(48.0)
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member]
Revenue		1,935.4	2,117.8	1,747.7
Changes in accrued revenue under alternative revenue programs		10.7	1.5	4.3
Total Gas Utility operating revenues		1,946.1	2,119.3	1,752.0
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Residential [Member]
Revenue		1,416.6	1,234.0	1,184.3
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Commercial and Industrial [Member]
Revenue		338.9	586.0	383.0
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Transportation [Member]
Revenue		118.0	122.9	115.8
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Off-system and Other Inventive [Member]
Revenue		42.0	152.7	38.4
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Other Customer Revenue [Member]
Revenue		19.9	22.2	26.2
Spire [Member] \| Gas Marketing [Member] \| Operating Segments [Member]
Unregulated Operating Revenue		234.9	96.5	87.9
Spire [Member] \| Other Segments [Member] \| Operating Segments [Member]
Unregulated Operating Revenue		69.2	67.7	57.8
Spire Missouri [Member]
Changes in accrued revenue under alternative revenue programs		12.8	3.0	2.3
Total Gas Utility operating revenues	$ 100.0
Operating Revenues		1,321.0	1,516.6	1,193.6
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member]
Revenue		1,308.2	1,513.6	1,191.3
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Residential [Member]
Revenue		1,061.4	882.1	859.6
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Commercial and Industrial [Member]
Revenue		177.2	436.1	241.4
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Transportation [Member]
Revenue		33.3	33.5	32.9
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Off-system and Other Inventive [Member]
Revenue		25.2	145.6	35.1
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Other Customer Revenue [Member]
Revenue		11.1	16.3	22.3
Spire Alabama Inc [Member]
Changes in accrued revenue under alternative revenue programs		1.7	3.4	(0.2)
Operating Revenues		509.1	494.0	455.0
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member]
Revenue		507.4	490.6	455.2
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Residential [Member]
Revenue		291.6	288.0	267.8
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Commercial and Industrial [Member]
Revenue		119.1	114.9	109.4
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Transportation [Member]
Revenue		74.4	78.7	72.9
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Off-system and Other Inventive [Member]
Revenue		16.8	7.1	3.2
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Other Customer Revenue [Member]
Revenue		$ 5.5	$ 1.9	$ 1.9

Revenue recognition changes in accrued revenue under alternative revenue programs.

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The amount of unregulated operating revenues recognized during the period.

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