Amount of impairment loss from asset representing future economic benefit arising from other asset acquired in business combination or from joint venture formation or both, that is not individually identified and separately recognized.

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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+ Details

Divestitures - Schedule of Information Related to Discontinued Operations Assets and Liabilities (Parenthetical) (Details) - USD ($) $ in Millions	6 Months Ended	9 Months Ended
	Mar. 31, 2026	Jun. 30, 2026	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024
Disposal Group, Including Discontinued Operations [Line Items]
Net allowance of account receivable	$ 33.7	$ 30.4	$ 28.8	$ 33.8	$ 36.8	$ 31.4
Spire Mississippi [Member]
Disposal Group, Including Discontinued Operations [Line Items]
Goodwill impairment	$ 3.9
Discontinued Operations [Member] \| Spire Marketing [Member]
Disposal Group, Including Discontinued Operations [Line Items]
Non-utility property, accumulated depreciation		7.1		7.0
Discontinued Operations [Member] \| Spire Storage [Member]
Disposal Group, Including Discontinued Operations [Line Items]
Non-utility property, accumulated depreciation		15.7		$ 12.3
Discontinued Operations [Member] \| Spire Mississippi [Member]
Disposal Group, Including Discontinued Operations [Line Items]
Net allowance of account receivable		0.1
Goodwill impairment		$ 3.9