Pension Plans and Other Postretirement Benefits - Additional Information (Details)	12 Months Ended
	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($) plan	Sep. 30, 2020 USD ($) plan	Sep. 30, 2019 USD ($)	Apr. 19, 2018 USD ($)	Apr. 18, 2018 USD ($)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Settlement benefits paid		$ 0
Implementation period used to calculate return on plan assets		4 years	4 years
Gains or losses includible in cost amortized to extent exceeds benefit obligations or market-related value of plan assets, percentage		10.00%	10.00%
Regulatory assets		$ 1,300,000,000.0	$ 1,138,900,000
Remaining recovery period for regulatory assets for which no return on investment during recovery period is provided		15 years
Medical insurance available until age is reached after early retirement		65 years
Recovery in rates for postretirement benefit						$ 8,600,000
401(K) plans, cost of defined contributions		$ 15,500,000	$ 13,600,000	$ 13,800,000
Pension Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rates		3.00%	3.00%
Settlement benefits paid		$ 67,600,000	$ 89,300,000
Employer contributions		53,400,000	43,700,000
Spire Alabama and Spire Missouri | Pension Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Settlement benefits paid		67,500,000
Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory assets		759,400,000	580,800,000
401(K) plans, cost of defined contributions		$ 10,900,000	$ 9,500,000	$ 10,000,000.0
Spire Missouri | Scenario Forecast
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Anticipated Contributions to pension plans for qualified trust	$ 0
Spire Missouri | Pension Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Number Of Plans | plan		2	2
Discount rates		3.00%	2.85%	3.20%
Settlement benefits paid		$ 44,600,000	$ 74,500,000
Anticipated Contributions to pension plans for qualified trust		37,600,000
Anticipated contributions to pension plans for non-qualified plans		800,000
Employer contributions		$ 42,200,000	30,300,000
Spire Missouri | Pension Plans | Change In Benefit Obligations
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Number Of Plans | plan		1
Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory assets		$ 502,100,000	510,300,000
401(K) plans, cost of defined contributions		$ 2,900,000	$ 3,400,000	$ 3,100,000
Spire Alabama | Scenario Forecast
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Anticipated Contributions to pension plans for qualified trust	$ 0
Spire Alabama | Pension Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Number Of Plans | plan		1	1
Discount rates		3.10%	2.95%	3.20%
Settlement benefits paid		$ 22,900,000	$ 14,800,000
Settlement losses amortized over remaining actuarial life		11 years 8 months 12 days	11 years 4 months 24 days
Anticipated Contributions to pension plans for qualified trust		$ 14,400,000
Employer contributions		11,100,000	$ 12,700,000
Spire Missouri West | Pension Cost | MoPSC | Infrastructure System Replacement Surcharge
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory assets					$ 5,500,000	9,900,000
Spire Missouri West | Pension and Other Postretirement Benefits
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Amortization of assets		$ 26,200,000
Spire Missouri East | Pension Cost | MoPSC | Infrastructure System Replacement Surcharge
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory assets					$ 29,000,000.0	$ 15,500,000
Spire Missouri East | Pension and Other Postretirement Benefits
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Remaining recovery period for regulatory assets for which no return on investment during recovery period is provided		8 years
Amortization of assets		$ 173,000,000.0