Regulatory Matters - Additional Information (Details) $ in Millions					6 Months Ended	7 Months Ended
	Jan. 14, 2019 USD ($)	Nov. 30, 2018 USD ($)	Sep. 28, 2018 USD ($)	Apr. 25, 2018 USD ($)	Mar. 31, 2019 USD ($) mi $ / MMBTU	Jan. 31, 2019 USD ($)
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
Length of dual 20-inch diameter pipeline | mi					10.1
Spire Missouri
Public Utilities, General Disclosures [Line Items]
Increase in negotiated rate per day | $ / MMBTU					0.02
Spire Alabama
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease) amount					$ (3.3)
Public utilities, requested rate increase (decrease), amount		$ 8.7
Infrastructure System Replacement Surcharge | Spire Missouri East
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease) amount			$ 2.6
Applications requests for the approval of revenue related to commission amount						$ 7.4
Infrastructure System Replacement Surcharge | Spire Missouri West
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease) amount			$ 5.4
Applications requests for the approval of revenue related to commission amount						$ 7.4
Infrastructure System Replacement Surcharge | Spire Missouri
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount	$ 3.2
Infrastructure System Replacement Surcharge | MoPSC
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), costs from buildings sold in 2014 excluded from rate base				$ 1.8
Rate case expenses				0.9
Pension Cost | Infrastructure System Replacement Surcharge | MoPSC
Public Utilities, General Disclosures [Line Items]
Regulatory assets recovery				$ 28.8