Financing Arrangements and Long-term Debt - Additional Information (Details)			3 Months Ended
	Dec. 15, 2020 USD ($)	Mar. 26, 2020 USD ($) bank	Dec. 31, 2020 USD ($)	Dec. 14, 2016 bank
Line of Credit Facility [Line Items]
Long-term Debt			$ 975,000,000.0
Liabilities | Lender Concentration Risk
Line of Credit Facility [Line Items]
Line of credit facility, number of banks in agreement | bank				11
Spire
Line of Credit Facility [Line Items]
Term loan bear interest rate per annum			0.40%
Short-term borrowings used to support lending to Utilities			$ 455,500,000
Spire | Term Loan
Line of Credit Facility [Line Items]
Line of credit facility, number of banks in agreement | bank		2
Long-term Debt		$ 150,000,000.0
Team loan interest rate description			The term loan bore interest at the LIBOR Rate (as defined in the loan agreement) plus 0.85% per annum.
Term loan bear interest rate per annum			1.10%
Spire | Term Loan | LIBOR
Line of Credit Facility [Line Items]
Term loan bear interest rate per annum		0.85%
Spire Alabama | Senior Notes | Private Placement | Series 2020 Senior Notes due 2030
Line of Credit Facility [Line Items]
Long-term debt	$ 150,000,000.0
Stated interest rate	2.04%
Debt instrument, maturity date	Dec. 15, 2030
Debt instrument, payment terms			Interest is payable semi-annually.
Revolving Credit Facility Borrowings
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity			$ 975,000,000.0
Minimum required ratio of earnings before interest, taxes, depreciation, and amortization (EBITDA) times interest expense as required by the line of credit covenant			70.00%
Revolving Credit Facility Borrowings | Maximum
Line of Credit Facility [Line Items]
Debt to total capitalization ratio			0.60
Revolving Credit Facility Borrowings | Spire
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity			$ 300,000,000.0
Revolving Credit Facility Borrowings | Spire Missouri
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity			475,000,000.0
Revolving Credit Facility Borrowings | Spire Alabama
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity			200,000,000.0
Commercial Paper Notes
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity			$ 975,000,000.0
Debt term			365 days
Commercial Paper Notes | Spire
Line of Credit Facility [Line Items]
Term loan bear interest rate per annum			0.20%