CONSOLIDATED STATEMENTS OF CAPITALIZATION (Parenthetical) - $ / shares	Sep. 30, 2018	Sep. 30, 2017
Long - Term Debt
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, authorized (in shares)	70,000,000	70,000,000
Common stock, outstanding (in shares)	50,671,903	48,263,243
Spire Missouri
Long - Term Debt
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, authorized (in shares)	50,000,000	50,000,000
Common stock, outstanding (in shares)	24,577	24,577
Spire Missouri | 5.5% Series, due May 1, 2019
Long - Term Debt
Debt instrument, interest rate, stated percentage	5.50%	5.50%
Spire Missouri | 3.0% Series, due March 15, 2023
Long - Term Debt
Debt instrument, interest rate, stated percentage	3.00%	3.00%
Spire Missouri | 3.4% Series, due August 15, 2023
Long - Term Debt
Debt instrument, interest rate, stated percentage	3.40%	3.40%
Spire Missouri | 3.4% Series, due March 15, 2028
Long - Term Debt
Debt instrument, interest rate, stated percentage	3.40%	3.40%
Spire Missouri | 7.0% Series, due June 1, 2029
Long - Term Debt
Debt instrument, interest rate, stated percentage	7.00%	7.00%
Spire Missouri | 7.9% Series, due September 15, 2030
Long - Term Debt
Debt instrument, interest rate, stated percentage	7.90%	7.90%
Spire Missouri | 6.0% Series, due May 1, 2034
Long - Term Debt
Debt instrument, interest rate, stated percentage	6.00%	6.00%
Spire Missouri | 6.15% Series, due June 1, 2036
Long - Term Debt
Debt instrument, interest rate, stated percentage	6.15%	6.15%
Spire Missouri | 4.625% Series, due August 15, 2043
Long - Term Debt
Debt instrument, interest rate, stated percentage	4.625%	4.625%
Spire Missouri | 3.68% Series, due September 15, 2032
Long - Term Debt
Debt instrument, interest rate, stated percentage	3.68%	3.68%
Spire Missouri | 4.23% Series, due September 15, 2047
Long - Term Debt
Debt instrument, interest rate, stated percentage	4.23%	4.23%
Spire Missouri | 4.38% Series, due September 15, 2057
Long - Term Debt
Debt instrument, interest rate, stated percentage	4.38%	4.38%
Spire Alabama
Long - Term Debt
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized (in shares)	3,000,000	3,000,000
Common stock, outstanding (in shares)	1,972,052	1,972,052
Spire Alabama | 5.2% Notes, due January 15, 2020
Long - Term Debt
Debt instrument, interest rate, stated percentage	5.20%	5.20%
Spire Alabama | 3.86% Notes, due December 22, 2021
Long - Term Debt
Debt instrument, interest rate, stated percentage	3.86%	3.86%
Spire Alabama | 3.21% Notes, due September 15, 2025
Long - Term Debt
Debt instrument, interest rate, stated percentage	3.21%	3.21%
Spire Alabama | 5.9% Notes, due January 15, 2037
Long - Term Debt
Debt instrument, interest rate, stated percentage	5.90%	5.90%
Spire Alabama | 4.31% Notes, due December 1, 2045
Long - Term Debt
Debt instrument, interest rate, stated percentage	4.31%	4.31%
Spire Alabama | 3.92% Notes, due January 15, 2048
Long - Term Debt
Debt instrument, interest rate, stated percentage	3.92%	3.92%
Spire Alabama | 4.02% Notes, due January 15, 2058
Long - Term Debt
Debt instrument, interest rate, stated percentage	4.02%	4.02%
Other | 3.10% Note, due December 30, 2018
Long - Term Debt
Debt instrument, interest rate, stated percentage	3.10%	3.10%
Other | 4.14% First Mortgage Bonds, due September 30, 2021
Long - Term Debt
Debt instrument, interest rate, stated percentage	4.14%	4.14%
Other | 5.00% First Mortgage Bonds, due September 30, 2031
Long - Term Debt
Debt instrument, interest rate, stated percentage	5.00%	5.00%
Spire | 2.55% Senior Notes, due August 15, 2019
Long - Term Debt
Debt instrument, interest rate, stated percentage	2.55%	2.55%
Spire | 2.52% Senior Notes, due September 1, 2021
Long - Term Debt
Debt instrument, interest rate, stated percentage	2.52%	2.52%
Spire | 3.31% Notes Payable, due December 15, 2022
Long - Term Debt
Debt instrument, interest rate, stated percentage	3.31%	3.31%
Spire | 3.54% Senior Notes, due February 27, 2024
Long - Term Debt
Debt instrument, interest rate, stated percentage	3.54%	3.54%
Spire | 3.13% Senior Notes, due September 1, 2026
Long - Term Debt
Debt instrument, interest rate, stated percentage	3.13%	3.13%
Spire | 3.93% Senior Notes, due March 15, 2027
Long - Term Debt
Debt instrument, interest rate, stated percentage	3.93%	3.93%
Spire | 4.70% Senior Notes, due August 15, 2044
Long - Term Debt
Debt instrument, interest rate, stated percentage	4.70%	4.70%