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v3.21.1

Financing - Additional Information (Details) |  |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended |
--- | --- | --- | --- | --- | --- | --- | ---
Mar. 23, 2021 USD ($) | Dec. 15, 2020 USD ($) | Mar. 26, 2020 USD ($) bank | Feb. 28, 2021 USD ($) $ / shares shares | Mar. 31, 2021 USD ($) | Mar. 31, 2020 USD ($) shares | Mar. 31, 2021 USD ($) | Mar. 31, 2020 USD ($) shares | Dec. 14, 2016 bank
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Long-term Debt |  |  |  |  | $ 975,000,000.0 |  | $ 975,000,000.0 |  |
Common stock issued |  |  |  |  |  | $ 9,500,000 |  | $ 9,500,000 |
Common Stock $1.00 par value |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | shares |  |  |  |  |  | 112,758 |  | 112,758 |
Common stock issued |  |  |  |  |  | $ 100,000 |  | $ 100,000 |
Liabilities | Lender Concentration Risk |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Line of credit facility, number of banks in agreement | bank |  |  |  |  |  |  |  |  | 11
Spire |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Term loan bear interest rate per annum |  |  |  |  |  |  | 0.40% |  |
Short-term borrowings used to support lending to Utilities |  |  |  |  | 398,100,000 |  | $ 398,100,000 |  |
Present value of stock purchase contract payment recorded as liability |  |  |  |  | 35,000,000.0 |  |  |  |
Spire | Common Stock $1.00 par value |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Price divided by applicable market value to determine number of shares per stock purchase contract | $ / shares |  |  |  | $ 50.00 |  |  |  |  |
Spire | 2021 Series A 0.75% Remarketable Senior Notes |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Stated interest rate |  |  |  | 0.75% |  |  |  |  |
Debt instrument, maturity date |  |  |  | Mar. 01, 2026 |  |  |  |  |
Debt instrument, payment terms |  |  |  | The Company will make quarterly interest payments on the RSNs at the rate of 0.75% per year and quarterly contract adjustment payments on the stock purchase contracts at the rate of 6.75%. |  |  |  |  |
Common stock issued (in shares) | shares |  |  |  | 3,500,000 |  |  |  |  |
Common stock issued |  |  |  | $ 175,000,000.0 |  |  |  |  |
Net proceeds after underwriting fees and other issuance costs |  |  |  | $ 169,300,000 |  |  |  |  |
Units price | $ / shares |  |  |  | $ 50 |  |  |  |  |
Percentage of undivided beneficial ownership interest |  |  |  | 5.00% |  |  |  |  |
Principal amount |  |  |  | $ 1,000 |  |  |  |  |
Stock purchase contracts rate |  |  |  | 6.75% |  |  |  |  |
Spire | 2021 Series A 0.75% Remarketable Senior Notes | Stock Purchase Contract |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Units price | $ / shares |  |  |  | $ 50 |  |  |  |  |
Spire | Term Loan |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [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 |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Term loan bear interest rate per annum |  |  | 0.85% |  |  |  |  |  |
Spire | Senior Notes | 2021 Series A 0.75% Remarketable Senior Notes |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Debt amount |  |  |  | $ 175,000,000.0 |  |  |  |  |
Stated interest rate |  |  |  | 0.75% |  |  |  |  |
Spire | Maximum | Common Stock $1.00 par value |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Number of shares to be purchased per stock purchase contract, settlement rate | shares |  |  |  | 0.7783 |  |  |  |  |
Spire | Minimum | Common Stock $1.00 par value |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Number of shares to be purchased per stock purchase contract, settlement rate | shares |  |  |  | 0.6354 |  |  |  |  |
Spire Missouri | Term Loan |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Term loan bear interest rate per annum |  |  |  |  |  |  | 0.80% |  |
Spire Alabama | Senior Notes | Private Placement | Series 2020 Senior Notes due 2030 |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [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 |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Line of credit facility borrowing capacity |  |  |  |  | $ 975,000,000.0 |  | $ 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% |  | 70.00% |  |
Revolving Credit Facility Borrowings | Maximum |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Debt to total capitalization ratio |  |  |  |  | 0.60 |  | 0.60 |  |
Revolving Credit Facility Borrowings | Spire |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Line of credit facility borrowing capacity |  |  |  |  | $ 300,000,000.0 |  | $ 300,000,000.0 |  |
Revolving Credit Facility Borrowings | Spire Missouri |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Line of credit facility borrowing capacity |  |  |  |  | 475,000,000.0 |  | 475,000,000.0 |  |
Revolving Credit Facility Borrowings | Spire Alabama |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Line of credit facility borrowing capacity |  |  |  |  | 200,000,000.0 |  | 200,000,000.0 |  |
Commercial Paper Notes |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Debt amount |  |  |  |  | $ 975,000,000.0 |  | $ 975,000,000.0 |  |
Debt term |  |  |  |  |  |  | 365 days |  |
Commercial Paper Notes | Spire |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Term loan bear interest rate per annum |  |  |  |  |  |  | 0.30% |  |
Unsecured Term Loan | Spire Missouri |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Debt amount | $ 250,000,000.0 |  |  |  |  |  |  |  |
Debt term | 364 days |  |  |  |  |  |  |  |
Prepayment penalty | $ 0 |  |  |  |  |  |  |  |
Unsecured Term Loan | Spire Missouri | LIBOR |  |  |  |  |  |  |  |  |
Debt Instrument And Equity Units [Line Items] |  |  |  |  |  |  |  |  |
Interest rate | 0.65% |  |  |  |  |  |  |  |

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