Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

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-Topic 850
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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.

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Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 220
-Section S99
-Paragraph 1
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-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
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-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

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Summary of Significant Accounting Policies - Schedule of Inter-Company Transactions (Details) - Affiliated Entity - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Spire Marketing Inc \| Spire Missouri \| Regulated Operation
Related Party Transaction [Line Items]
Purchases of natural gas from related party	$ 9.2	$ 10.9	$ 77.5	$ 43.7
Sales of natural gas to Spire Marketing Inc.			1.1
Spire Marketing Inc \| Spire Alabama \| Regulated Operation
Related Party Transaction [Line Items]
Purchases of natural gas from related party		0.8	10.6	5.1
Sales of natural gas to Spire Marketing Inc.		0.3	0.1	0.3
Spire STL Pipeline LLC \| Spire Missouri \| Unregulated Operation
Related Party Transaction [Line Items]
Transportation services received	$ 7.9	8.0	23.9	19.8
Spire NGL Inc. \| Spire Missouri \| Unregulated Operation
Related Party Transaction [Line Items]
Transportation services received		$ 0.3	$ 0.5	$ 0.8