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Fair Value Measurements | 12 Months Ended
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Sep. 30, 2025
Fair Value Disclosures [Abstract] |
Fair Value Measurements | 9. FAIR VALUE MEASUREMENTS The information presented below categorizes the assets and liabilities in the balance sheets that are accounted for at fair value on a recurring basis in periods subsequent to initial recognition. The mutual funds and bonds included in Level 1 are valued based on exchange-quoted market prices of individual securities. Derivative instruments included in Level 1 are valued using quoted market prices on the NYMEX or the ICE and also certain natural gas commodity contracts. Derivative instruments classified in Level 2 include physical commodity derivatives and interest rate swaps that are valued using broker or dealer quotation services whose prices are derived principally from, or are corroborated by, observable market inputs. Also included in Level 2 are certain derivative instruments that have values that are similar to, and correlate with, quoted prices for exchange-traded instruments in active markets. Derivative instruments included in Level 3 are valued using generally unobservable inputs that are based upon the best information available and reflect management’s assumptions about how market participants would price the asset or liability. There were no Level 3 balances as of September 30, 2025 or 202 4. The Company’s and the Utilities’ policy is to recognize transfers between the levels of the fair value hierarchy, if any, as of the beginning of the interim reporting period in which circumstances change or events occur to cause the transfer. The mutual funds are included in “Other investments” on the Company’s balance sheets and in “Other Property and Investments” on Spire Missouri’s balance sheets. Changes in their recurring valuations are recorded as unrealized investment gains or losses in the corresponding periodic income statement. Derivative assets and liabilities, including receivables and payables associated with cash margin requirements, are presented net on the balance sheets when a legally enforceable netting agreement exist between the Company, Spire Missouri or Spire Alabama and the counterparty to the derivative contract. For additional information on derivative instruments, see Note 10, Derivative Instruments and Hedging Activities. Spire
|  |  |  |  |  |  |  |  |  |  | Effects of |  |  |  |
|  | Quoted |  |  |  |  |  |  |  |  | Netting |  |  |  |
|  | Prices |  |  | Significant |  |  | Significant |  |  | and Cash |  |  |  |
|  | in Active |  |  | Observable |  |  | Unobservable |  |  | Margin |  |  |  |
|  | Markets |  |  | Inputs |  |  | Inputs |  |  | Receivables |  |  |  |
|  | (Level 1) |  |  | (Level 2) |  |  | (Level 3) |  |  | /Payables |  |  | Total |
As of September 30, 2025 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ASSETS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Utility: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. stock/bond mutual funds |  | $ | 27.5 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 27.5 |
NYMEX/ICE natural gas contracts |  |  | 2.9 |  |  |  | — |  |  |  | — |  |  |  | (2.9 | ) |  |  | — |
Gas Marketing: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  |  | 11.4 |  |  |  | — |  |  |  | — |  |  |  | (11.4 | ) |  |  | — |
Natural gas commodity contracts |  |  | — |  |  |  | 44.8 |  |  |  | — |  |  |  | (2.7 | ) |  |  | 42.1 |
Other: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. stock/bond mutual funds |  |  | 27.0 |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 27.0 |
U.S. bonds |  |  | 23.5 |  |  |  | — |  |  |  | — |  |  |  |  |  |  | 23.5 |
Global Bonds |  |  | 1.5 |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 1.5 |
Interest rate swaps |  |  | — |  |  |  | 10.0 |  |  |  | — |  |  |  | — |  |  |  | 10.0 |
Total |  | $ | 93.8 |  |  | $ | 54.8 |  |  | $ | — |  |  | $ | (17.0 | ) |  | $ | 131.6 |
LIABILITIES |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Utility: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  | $ | 25.9 |  |  | $ | — |  |  | $ | — |  |  | $ | (1.3 | ) |  | $ | 24.6 |
Gas Marketing: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  |  | 19.0 |  |  |  | — |  |  |  | — |  |  |  | (19.0 | ) |  |  | — |
Natural gas commodity contracts |  |  | — |  |  |  | 16.7 |  |  |  | — |  |  |  | (2.7 | ) |  |  | 14.0 |
Total |  | $ | 44.9 |  |  | $ | 16.7 |  |  | $ | — |  |  | $ | (23.0 | ) |  | $ | 38.6 |
As of September 30, 2024 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ASSETS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Utility: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. stock/bond mutual funds |  | $ | 24.3 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 24.3 |
NYMEX/ICE natural gas contracts |  |  | 3.4 |  |  |  | — |  |  |  | — |  |  |  | (3.4 | ) |  |  | — |
Gas Marketing: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  |  | 7.0 |  |  |  | — |  |  |  | — |  |  |  | (7.0 | ) |  |  | — |
Natural gas commodity contracts |  |  | — |  |  |  | 46.0 |  |  |  | — |  |  |  | (3.5 | ) |  |  | 42.5 |
Other: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. stock/bond mutual funds |  |  | 17.9 |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 17.9 |
U.S. bonds |  |  | 21.9 |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 21.9 |
Global Bonds |  |  | 5.9 |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 5.9 |
Interest rate swaps |  |  | — |  |  |  | 0.8 |  |  |  | — |  |  |  | — |  |  |  | 0.8 |
Total |  | $ | 80.4 |  |  | $ | 46.8 |  |  | $ | — |  |  | $ | (13.9 | ) |  | $ | 113.3 |
LIABILITIES |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Utility: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  | $ | 13.6 |  |  | $ | — |  |  | $ | — |  |  | $ | (3.8 | ) |  | $ | 9.8 |
Gas Marketing: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  |  | 17.7 |  |  |  | — |  |  |  | — |  |  |  | (17.7 | ) |  |  | — |
Natural gas commodity contracts |  |  | — |  |  |  | 24.5 |  |  |  | — |  |  |  | (3.5 | ) |  |  | 21.0 |
Other: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate swaps |  |  | — |  |  |  | 1.5 |  |  |  | — |  |  |  | — |  |  |  | 1.5 |
Total |  | $ | 31.3 |  |  | $ | 26.0 |  |  | $ | — |  |  | $ | (25.0 | ) |  | $ | 32.3 |
Spire Missouri
|  |  |  |  |  |  |  |  |  |  | Effects of |  |  |  |
|  | Quoted |  |  |  |  |  |  |  |  | Netting |  |  |  |
|  | Prices |  |  | Significant |  |  | Significant |  |  | and Cash |  |  |  |
|  | in Active |  |  | Observable |  |  | Unobservable |  |  | Margin |  |  |  |
|  | Markets |  |  | Inputs |  |  | Inputs |  |  | Receivables |  |  |  |
|  | (Level 1) |  |  | (Level 2) |  |  | (Level 3) |  |  | /Payables |  |  | Total |
As of September 30, 2025 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ASSETS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. stock/bond mutual funds |  | $ | 27.5 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 27.5 |
NYMEX/ICE natural gas contracts |  |  | 2.9 |  |  |  | — |  |  |  | — |  |  |  | (2.9 | ) |  |  | — |
Total |  | $ | 30.4 |  |  | $ | — |  |  | $ | — |  |  | $ | (2.9 | ) |  | $ | 27.5 |
LIABILITIES |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  | $ | 25.9 |  |  | $ | — |  |  | $ | — |  |  | $ | (1.3 | ) |  | $ | 24.6 |
As of September 30, 2024 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ASSETS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. stock/bond mutual funds |  | $ | 24.3 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 24.3 |
NYMEX/ICE natural gas contracts |  |  | 3.4 |  |  |  | — |  |  |  | — |  |  |  | (3.4 | ) |  |  | — |
Total |  | $ | 27.7 |  |  | $ | — |  |  | $ | — |  |  | $ | (3.4 | ) |  | $ | 24.3 |
LIABILITIES |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  | $ | 13.6 |  |  | $ | — |  |  | $ | — |  |  | $ | (3.8 | ) |  | $ | 9.8 |
Spire Alabama Spire Alabama occasionally utilizes a gasoline derivative program to stabilize the cost of fuel used in operations. As of September 30, 2025 and September 30, 2024, there were no gasoline derivatives outstanding.

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- Definition The entire disclosure of the fair value measurement of assets and liabilities, which includes financial instruments measured at fair value that are classified in shareholders' equity, which may be measured on a recurring or nonrecurring basis. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org/820/tableOfContent + Details
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