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The total amount of operating revenues recognized during the period.

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The amount of regulated gas operating revenues recognized during the period.

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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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Revenue - Schedule of Revenue Disaggregated by Source and Customer Type (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Disaggregation of Revenue [Line Items]
Total Operating Revenues	$ 421.9	$ 414.1	$ 2,142.3	$ 2,299.2
Consolidation, Eliminations [Member]
Disaggregation of Revenue [Line Items]
Total Operating Revenues	(16.6)	(17.1)	(48.0)	(46.8)
Gas Utility [Member] \| Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Total Operating Revenues	347.5	372.7	1,931.2	2,160.6
Gas Marketing [Member] \| Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Total Operating Revenues	43.1	21.2	129.7	103.5
Midstream [Member] \| Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Total Operating Revenues	42.2	32.5	114.1	68.9
Other Operating Segment [Member]
Disaggregation of Revenue [Line Items]
Total Operating Revenues	5.7	4.8	15.3	13.0
Spire Missouri [Member]
Disaggregation of Revenue [Line Items]
Changes in accrued revenue under alternative revenue programs	4.0	8.0	22.5	49.3
Total Operating Revenues	230.1	248.8	1,359.2	1,550.7
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Revenue	226.1	240.8	1,336.7	1,501.4
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Residential [Member]
Disaggregation of Revenue [Line Items]
Revenue	155.8	169.5	967.6	1,091.2
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue	46.9	52.6	288.4	348.5
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Transportation [Member]
Disaggregation of Revenue [Line Items]
Revenue	7.9	7.5	28.1	26.6
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Off-system and Other Incentive [Member]
Disaggregation of Revenue [Line Items]
Revenue	12.0	7.0	41.4	23.4
Spire Missouri [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Other Customer Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue	3.5	4.2	11.2	11.7
Spire Alabama Inc [Member]
Disaggregation of Revenue [Line Items]
Changes in accrued revenue under alternative revenue programs	(0.8)	(0.2)	(6.2)	(5.2)
Total Operating Revenues	98.8	103.5	471.6	505.1
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Revenue	99.6	103.7	477.8	510.3
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Residential [Member]
Disaggregation of Revenue [Line Items]
Revenue	48.3	53.0	280.2	306.7
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue	24.7	26.9	116.1	130.4
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Transportation [Member]
Disaggregation of Revenue [Line Items]
Revenue	20.5	20.3	66.8	65.1
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Off-system and Other Incentive [Member]
Disaggregation of Revenue [Line Items]
Revenue	5.0	2.6	9.8	5.6
Spire Alabama Inc [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Other Customer Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue	1.1	0.9	4.9	2.5
Spire [Member]
Disaggregation of Revenue [Line Items]
Total Operating Revenues	421.9	414.1	2,142.3	2,299.2
Spire [Member] \| Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Total Operating Revenues	438.5	431.2	2,190.3	2,346.0
Spire [Member] \| Consolidation, Eliminations [Member]
Disaggregation of Revenue [Line Items]
Total Operating Revenues	(16.6)	(17.1)	(48.0)	(46.8)
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Revenue	345.0	365.9	1,914.4	2,116.5
Changes in accrued revenue under alternative revenue programs	2.5	6.8	16.8	44.1
Total Gas Utility operating revenues	347.5	372.7	1,931.2	2,160.6
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Residential [Member]
Disaggregation of Revenue [Line Items]
Revenue	212.0	232.2	1,302.9	1,454.5
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue	79.5	87.3	438.1	513.1
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Transportation [Member]
Disaggregation of Revenue [Line Items]
Revenue	30.9	30.3	102.9	99.7
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Off-system and Other Incentive [Member]
Disaggregation of Revenue [Line Items]
Revenue	17.0	9.6	51.2	29.0
Spire [Member] \| Gas Utility [Member] \| Operating Segments [Member] \| Other Customer Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue	5.6	6.5	19.3	20.2
Spire [Member] \| Gas Marketing [Member] \| Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Unregulated Operating Revenue	43.1	21.2	129.7	103.5
Spire [Member] \| Midstream [Member] \| Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Unregulated Operating Revenue	42.2	32.5	114.1	68.9
Spire [Member] \| Other Operating Segment [Member] \| Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Unregulated Operating Revenue	$ 5.7	$ 4.8	$ 15.3	$ 13.0