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Regulatory Matters - Additional Information (Details) - USD ($)				1 Months Ended		3 Months Ended
	Jan. 03, 2022	Dec. 23, 2021	Aug. 23, 2021	Oct. 31, 2021	Feb. 28, 2021	Dec. 31, 2021	Dec. 31, 2020	Jan. 12, 2022	Dec. 22, 2021	Jul. 29, 2020
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					$ 195,800,000	$ 249,200,000	$ 181,200,000
Incremental gross revenue					$ 3,200,000
Spire STL Pipeline LLC
Public Utilities, General Disclosures [Line Items]
Impairment of assets						270,000,000
Spire Missouri
Public Utilities, General Disclosures [Line Items]
Natural gas						156,300,000	$ 161,600,000
Regulatory preferred stock and debt securities issuance, amount authorized										$ 660,000,000.0
Regulatory preferred stock and debt securities issuance, remaining authorized amount										$ 55,000,000.0
Spire Gulf
Public Utilities, General Disclosures [Line Items]
Approved return rate on equity				9.95%
Spire Mississippi
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), annualized revenue			$ 1,100,000
Subsequent Event \| Spire Gulf
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), annualized revenue	$ 1,000,000.0
Infrastructure System Replacement Surcharge \| Spire Missouri
Public Utilities, General Disclosures [Line Items]
Regulated operating revenue pipe replacement		$ 11,300,000
MoPSC
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease) amount		72,200,000
Requested rate increase		24,900,000
Estimated pre-tax impact, annually						$ 1,000,000.0
MoPSC \| Spire Missouri
Public Utilities, General Disclosures [Line Items]
Financing authority pending approval									$ 800,000,000.0
MoPSC \| Subsequent Event \| Minimum
Public Utilities, General Disclosures [Line Items]
Estimated pre-tax impact, annually								$ 20,000,000
MoPSC \| Subsequent Event \| Maximum
Public Utilities, General Disclosures [Line Items]
Estimated pre-tax impact, annually								$ 30,000,000
MoPSC \| Infrastructure System Replacement Surcharge
Public Utilities, General Disclosures [Line Items]
Requested rate increase		$ 47,300,000