Long-term Debt (Tables)

12 Months Ended

Sep. 30, 2025

Debt Disclosure [Abstract]

Schedule of Long-Term Debt Instruments

The composition of long-term debt as of September 30 is shown in the following tables.

	2025			2024
Spire
5.30% Senior Notes, due March 1, 2026	$	350.0		$	350.0
3.13% Senior Notes, due September 1, 2026		130.0			130.0
3.93% Senior Notes, due March 15, 2027		100.0			100.0
5.80% Senior Notes, due March 15, 2033		150.0			150.0
4.70% Senior Notes, due August 15, 2044		250.0			250.0
Total principal of Spire Missouri long-term debt (see below)		1,968.0			1,818.0
Total principal of Spire Alabama long-term debt (see below)		715.0			750.0
Other subsidiaries' long-term debt:
5.00% First Mortgage Bonds, due September 30, 2031		42.0			42.0
2.95% Notes, with annual principal payments through December 2034		104.1			111.1
5.61% First Mortgage Bonds, due October 15, 2037		30.0			30.0
3.52% First Mortgage Bonds, due September 30, 2049		40.0			40.0
Total principal of long-term debt		3,879.1			3,771.1
Less: Unamortized discounts and debt issuance costs		(22.2	)		(24.7	)
Less: Current portion		(487.5	)		(42.0	)
Long-term debt, excluding current portion	$	3,369.4		$	3,704.4
Spire Missouri
First Mortgage Bonds:
3.40% Series, due March 15, 2028	$	45.0		$	45.0
7.00% Series, due June 1, 2029		19.3			19.3
2.84% Series, due November 15, 2029		275.0			275.0
4.88% Series, due September 15, 2030		90.0			—
7.90% Series, due September 15, 2030		30.0			30.0
5.12% Series, due September 15, 2032		60.0			—
3.68% Series, due September 15, 2032		50.0			50.0
4.80% Series, due February 15, 2033		400.0			400.0
6.00% Series, due May 1, 2034		99.3			99.3
5.15% Series, due August 15, 2034		320.0			320.0
6.15% Series, due June 1, 2036		54.5			54.5
4.63% Series, due August 15, 2043		99.9			99.9
4.23% Series, due September 15, 2047		70.0			70.0
3.30% Series, due June 1, 2051		305.0			305.0
4.38% Series, due September 15, 2057		50.0			50.0
Total principal of Spire Missouri long-term debt		1,968.0			1,818.0
Less: Unamortized discounts and debt issuance costs		(14.4	)		(14.6	)
Spire Missouri long-term debt, excluding current portion	$	1,953.6		$	1,803.4
Spire Alabama
3.21% Notes, due September 15, 2025	$	—		$	35.0
5.32% Notes, due October 15, 2029		90.0			90.0
2.88% Notes, due December 1, 2029		100.0			100.0
2.04% Notes, due December 15, 2030		150.0			150.0
5.41% Notes, due October 15, 2032		85.0			85.0
5.90% Notes, due January 15, 2037		45.0			45.0
4.31% Notes, due December 1, 2045		80.0			80.0
3.92% Notes, due January 15, 2048		45.0			45.0
4.64% Notes, due January 15, 2049		90.0			90.0
4.02% Notes, due January 15, 2058		30.0			30.0
Total principal of Spire Alabama long-term debt		715.0			750.0
Less: Unamortized discounts and debt issuance costs		(3.3	)		(3.7	)
Less: Current portion		—			(35.0	)
Spire Alabama long-term debt, excluding current portion	$	711.7		$	711.3

Schedule of Maturities of Long-Term Debt

Maturities of long-term debt for Spire on a consolidated basis, Spire Missouri and Spire Alabama for the five fiscal years after September 30, 2025 are as follows:

	2026		2027		2028		2029		2030
Spire	$	487.5	$	108.1	$	53.6	$	28.5	$	594.9
Spire Missouri		—		—		45.0		19.3		395.0
Spire Alabama		—		—		—		—		190.0