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v3.20.2

Long-term Debt - Schedule of Composition of Long-term Debt (Parenthetical) (Details) | 12 Months Ended
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Sep. 30, 2020
Spire Missouri | Floating-rate note due December 1, 2021 |
Debt Instrument [Line Items] |
Debt instrument, maturity date | Dec. 01, 2021
Spire Missouri | 3.00% Series, due March 15, 2023 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 3.00%
Debt instrument, maturity date | Mar. 15, 2023
Spire Missouri | 3.40% Series, due August 15, 2023 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 3.40%
Debt instrument, maturity date | Aug. 15, 2023
Spire Missouri | 3.40% Series, due March 15, 2028 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 3.40%
Debt instrument, maturity date | Mar. 15, 2028
Spire Missouri | 2.84% Series, due November 15, 2029 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 2.84%
Debt instrument, maturity date | Nov. 15, 2029
Spire Missouri | 7.0% Series, due June 1, 2029 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 7.00%
Debt instrument, maturity date | Jun. 01, 2029
Spire Missouri | 7.90% Series, due September 15, 2030 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 7.90%
Debt instrument, maturity date | Sep. 15, 2030
Spire Missouri | 3.68% Series, due September 15, 2032 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 3.68%
Debt instrument, maturity date | Sep. 15, 2032
Spire Missouri | 6.00% Series, due May 1, 2034 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 6.00%
Debt instrument, maturity date | May 01, 2034
Spire Missouri | 6.15% Series, due June 1, 2036 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 6.15%
Debt instrument, maturity date | Jun. 01, 2036
Spire Missouri | 4.63% Series, due August 15, 2043 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 4.63%
Debt instrument, maturity date | Aug. 15, 2043
Spire Missouri | 4.23% Series, due September 15, 2047 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 4.23%
Debt instrument, maturity date | Sep. 15, 2047
Spire Missouri | 4.38% Series, due September 15, 2057 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 4.38%
Debt instrument, maturity date | Sep. 15, 2057
Spire Alabama | 5.20% Notes, due January 15, 2020 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 5.20%
Debt instrument, maturity date | Jan. 15, 2020
Spire Alabama | 3.86% Notes, due December 22, 2021 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 3.86%
Debt instrument, maturity date | Dec. 22, 2021
Spire Alabama | 3.21% Notes, due September 15, 2025 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 3.21%
Debt instrument, maturity date | Sep. 15, 2025
Spire Alabama | 2.88% Notes, due December 1, 2029 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 2.88%
Debt instrument, maturity date | Dec. 01, 2029
Spire Alabama | 5.90% Notes, due January 15, 2037 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 5.90%
Debt instrument, maturity date | Jan. 15, 2037
Spire Alabama | 4.31% Notes, due December 1, 2045 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 4.31%
Debt instrument, maturity date | Dec. 01, 2045
Spire Alabama | 3.92% Notes, due January 15, 2048 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 3.92%
Debt instrument, maturity date | Jan. 15, 2048
Spire Alabama | 4.64% Notes, due January 15, 2049 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 4.64%
Debt instrument, maturity date | Jan. 15, 2049
Spire Alabama | 4.02% Notes, due January 15, 2058 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 4.02%
Debt instrument, maturity date | Jan. 15, 2058
Spire | 2.52% Senior Notes, due September 1, 2021 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 2.52%
Debt instrument, maturity date | Sep. 01, 2021
Spire | 3.31% Notes Payable, due December 15, 2022 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 3.31%
Debt instrument, maturity date | Dec. 15, 2022
Spire | 3.54% Senior Notes, due February 27, 2024 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 3.54%
Debt instrument, maturity date | Feb. 27, 2024
Spire | 3.13% Senior Notes, due September 1, 2026 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 3.13%
Debt instrument, maturity date | Sep. 01, 2026
Spire | 3.93% Senior Notes, due March 15, 2027 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 3.93%
Debt instrument, maturity date | Mar. 15, 2027
Spire | 4.70% Senior Notes, due August 15, 2044 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 4.70%
Debt instrument, maturity date | Aug. 15, 2044
Subsidiaries | 4.14% First Mortgage Bonds, due September 30, 2021 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 4.14%
Debt instrument, maturity date | Sep. 30, 2021
Subsidiaries | 5.00% First Mortgage Bonds, due September 30, 2031 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 5.00%
Debt instrument, maturity date | Sep. 30, 2031
Subsidiaries | 2.95% Notes, with Annual Principal Payments through December 2034 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 2.95%
Debt instrument, maturity date | Dec. 31, 2034
Subsidiaries | 3.52% First Mortgage Bonds, due September 30, 2049 |
Debt Instrument [Line Items] |
Debt instrument, interest rate | 3.52%
Debt instrument, maturity date | Sep. 30, 2049

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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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