Note 2 - Revenue - Disaggregated of Revenue (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Operating Revenues	$ 418.5	$ 448.0	$ 2,355.9	$ 1,884.3
Operating Segments [Member]
Operating Revenues			38.7
Consolidation, Eliminations [Member]
Operating Revenues	(14.1)	(12.2)		(38.8)
Gas Utility [Member] \| Operating Segments [Member]
Operating Revenues	387.8	377.4	2,175.3	1,698.3
Gas Marketing [Member] \| Operating Segments [Member]
Operating Revenues	23.1	64.1	157.8	171.4
Midstream [Member] \| Operating Segments [Member]
Operating Revenues	17.4	14.6	49.1	41.3
Other Segments [Member]
Operating Revenues	4.3	4.1	12.4	12.1
Spire Missouri [Member]
Operating Revenues	253.8	236.7	1,586.0	1,155.8
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member]
Revenue	249.7	237.8	1,563.3	1,143.1
Changes in accrued revenue under alternative revenue programs	4.1	(1.1)	22.7	12.7
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Residential [Member]
Revenue	171.7	171.1	1,142.3	947.3
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Commercial and Industrial [Member]
Revenue	61.1	51.9	369.2	140.0
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Transportation [Member]
Revenue	7.1	7.1	26.1	26.4
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Off-system and Other Incentive [Member]
Revenue	6.0	4.5	15.6	20.3
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Other Customer Revenue [Member]
Revenue	3.8	3.2	10.1	9.1
Spire Alabama Inc [Member]
Operating Revenues	113.1	115.7	483.8	446.4
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member]
Revenue	111.3	104.7	483.9	436.1
Changes in accrued revenue under alternative revenue programs	1.8	11.0	(0.1)	10.3
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Residential [Member]
Revenue	56.7	56.2	288.1	266.2
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Commercial and Industrial [Member]
Revenue	32.7	24.0	127.8	101.6
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Transportation [Member]
Revenue	18.9	17.4	59.0	57.5
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Off-system and Other Incentive [Member]
Revenue	2.2	5.6	6.3	6.6
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Other Customer Revenue [Member]
Revenue	0.8	1.5	2.7	4.2
Spire [Member]
Operating Revenues	418.5	448.0	2,355.9	1,884.3
Spire [Member] \| Operating Segments [Member]
Operating Revenues	432.6	460.2	2,394.6	1,923.1
Spire [Member] \| Consolidation, Eliminations [Member]
Operating Revenues	(14.1)	(12.2)	(38.7)	(38.8)
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member]
Revenue	382.6	368.3	2,148.3	1,678.6
Changes in accrued revenue under alternative revenue programs	5.2	9.1	27.0	19.7
Total Gas Utility operating revenues	387.8	377.4	2,175.3	1,698.3
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Residential [Member]
Revenue	238.1	239.5	1,486.3	1,268.8
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Commercial and Industrial [Member]
Revenue	102.2	86.2	533.1	275.6
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Transportation [Member]
Revenue	29.0	26.9	93.2	91.6
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Off-system and Other Incentive [Member]
Revenue	8.2	10.1	21.9	26.9
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Other Customer Revenue [Member]
Revenue	5.1	5.6	13.8	15.7
Spire [Member] \| Gas Marketing [Member] \| Operating Segments [Member]
Unregulated Operating Revenue	23.1	64.1	157.8	171.4
Spire [Member] \| Midstream [Member] \| Operating Segments [Member]
Unregulated Operating Revenue	17.4	14.6	49.1	41.3
Spire [Member] \| Other Segments [Member] \| Operating Segments [Member]
Unregulated Operating Revenue	$ 4.3	$ 4.1	$ 12.4	$ 12.1

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+ References

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Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

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- Definition

The amount of unregulated operating revenues recognized during the period.

+ References

No definition available.

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