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Fair Value Measurements (Tables) | 12 Months Ended
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Sep. 30, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |
Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis | Spire
|  | Quoted Prices in Active Markets (Level 1) |  |  | Significant Observable Inputs (Level 2) |  |  | Significant Unobservable Inputs (Level 3) |  |  | Effects of Netting and Cash Margin Receivables /Payables |  |  | Total |
As of September 30, 2020 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ASSETS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Utility: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. stock/bond mutual funds |  | $ | 21.9 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 21.9 |
Gasoline and heating oil contracts |  |  | 0.3 |  |  |  | — |  |  |  | — |  |  |  | (0.3 | ) |  |  | — |
NYMEX/ICE natural gas contracts |  |  | 6.3 |  |  |  | — |  |  |  | — |  |  |  | (6.3 | ) |  |  | — |
Gas Marketing: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  |  | — |  |  |  | 27.7 |  |  |  | — |  |  |  | (25.4 | ) |  |  | 2.3 |
Natural gas commodity contracts |  |  | — |  |  |  | 14.5 |  |  |  | 0.4 |  |  |  | — |  |  |  | 14.9 |
Other: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. stock/bond mutual funds |  |  | 18.6 |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 18.6 |
Total |  | $ | 47.1 |  |  | $ | 42.2 |  |  | $ | 0.4 |  |  | $ | (32.0 | ) |  | $ | 57.7 |
LIABILITIES |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Utility: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  | $ | 0.9 |  |  | $ | — |  |  | $ | — |  |  | $ | (0.9 | ) |  | $ | — |
Gas Marketing: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  |  | 0.7 |  |  |  | 21.4 |  |  |  | — |  |  |  | (22.1 | ) |  |  | — |
Natural gas commodity contracts |  |  | — |  |  |  | 22.3 |  |  |  | — |  |  |  | — |  |  |  | 22.3 |
Other: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate swaps |  |  | — |  |  |  | 54.2 |  |  |  | — |  |  |  | — |  |  |  | 54.2 |
Total |  | $ | 1.6 |  |  | $ | 97.9 |  |  | $ | — |  |  | $ | (23.0 | ) |  | $ | 76.5 |
As of September 30, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ASSETS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Utility: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. stock/bond mutual funds |  | $ | 20.5 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 20.5 |
Gas Marketing: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  |  | 0.9 |  |  |  | 6.5 |  |  |  | — |  |  |  | (6.9 | ) |  |  | 0.5 |
Natural gas commodity contracts |  |  | — |  |  |  | 16.8 |  |  |  | — |  |  |  | (2.5 | ) |  |  | 14.3 |
Other: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. stock/bond mutual funds |  |  | 15.5 |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 15.5 |
Total |  | $ | 36.9 |  |  | $ | 23.3 |  |  | $ | — |  |  | $ | (9.4 | ) |  | $ | 50.8 |
LIABILITIES |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gas Utility: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  | $ | 12.3 |  |  | $ | — |  |  | $ | — |  |  | $ | (12.3 | ) |  | $ | — |
Gas Marketing: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  |  | 0.4 |  |  |  | 8.5 |  |  |  | — |  |  |  | (8.9 | ) |  |  | — |
Natural gas commodity contracts |  |  | — |  |  |  | 13.8 |  |  |  | 0.1 |  |  |  | (2.5 | ) |  |  | 11.4 |
Other: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate swaps |  |  | — |  |  |  | 43.4 |  |  |  | — |  |  |  | — |  |  |  | 43.4 |
Total |  | $ | 12.7 |  |  | $ | 65.7 |  |  | $ | 0.1 |  |  | $ | (23.7 | ) |  | $ | 54.8 |
Spire Missouri |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |
Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis | Spire Missouri
|  | Quoted Prices in Active Markets (Level 1) |  |  | Significant Observable Inputs (Level 2) |  |  | Significant Unobservable Inputs (Level 3) |  |  | Effects of Netting and Cash Margin Receivables /Payables |  |  | Total |
As of September 30, 2020 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ASSETS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. stock/bond mutual funds |  | $ | 21.9 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 21.9 |
Gasoline and heating oil contracts |  |  | 0.3 |  |  |  | — |  |  |  | — |  |  |  | (0.3 | ) |  |  | — |
NYMEX/ICE natural gas contracts |  |  | 6.3 |  |  |  | — |  |  |  | — |  |  |  | (6.3 | ) |  |  | — |
Total |  | $ | 28.5 |  |  | $ | — |  |  | $ | — |  |  | $ | (6.6 | ) |  | $ | 21.9 |
LIABILITIES |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  | $ | 0.9 |  |  | $ | — |  |  | $ | — |  |  | $ | (0.9 | ) |  | $ | — |
As of September 30, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ASSETS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. stock/bond mutual funds |  | $ | 20.5 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 20.5 |
LIABILITIES |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NYMEX/ICE natural gas contracts |  | $ | 12.3 |  |  | $ | — |  |  | $ | — |  |  | $ | (12.3 | ) |  | $ | — |

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- Definition Tabular disclosure of assets and liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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