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Regulatory Matters - Additional Information (Details) - USD ($) $ in Millions						1 Months Ended		3 Months Ended			6 Months Ended		7 Months Ended
	Apr. 21, 2022	Jan. 18, 2022	Jan. 03, 2022	Dec. 23, 2021	Aug. 23, 2021	Oct. 31, 2021	Feb. 28, 2021	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Dec. 22, 2021
Public Utilities, General Disclosures [Line Items]
Remaining recovery period for certain regulatory assets for which no return on investment during recovery period is provided (in years)								20 years
Remaining recovery period for regulatory assets for which no return on investment during recovery period is provided (in years)								15 years
Natural gas							$ 195.8	$ 392.0		$ 619.1	$ 641.2	$ 800.3
Incremental gross revenue							$ 3.2
Reduced revenue, accounts receivable, cost of gas and regulatory liabilities								150.0
Spire STL Pipeline LLC
Public Utilities, General Disclosures [Line Items]
Impairment of assets									$ 270.0
MoPSC \| Infrastructure System Replacement Surcharge
Public Utilities, General Disclosures [Line Items]
Requested rate increase				$ 47.3
Spire Missouri
Public Utilities, General Disclosures [Line Items]
Natural gas								287.8		$ 537.4	444.1	$ 699.0
Spire Missouri \| Infrastructure System Replacement Surcharge
Public Utilities, General Disclosures [Line Items]
Regulated operating revenue pipe replacement													$ 11.3
Spire Missouri \| MoPSC
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease) amount				72.2
Requested rate increase				$ 24.9
Amount deferred under order authorizing accounting treatment								17.5			17.5
Deferred amount in accordance with new capitalization rates								6.6			6.6
Deferred amount prudent costs in excess of capitalization rates								5.9			5.9
Deferred amount prudent costs related to the ISRS settlement								$ 5.0			5.0
Annual net increase in gas revenues											$ 151.9
Financing authority pending approval														$ 800.0
Spire Missouri \| MoPSC \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Incremental annual revenue from settlement	$ 8.5
Spire Gulf
Public Utilities, General Disclosures [Line Items]
Approved return rate on equity						9.95%
Approved rate increase (decrease), annualized revenue			$ 1.0
Spire Mississippi
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), annualized revenue		$ 0.8			$ 1.1