Note 6 - Long-term Debt (Tables)

12 Months Ended

Sep. 30, 2024

Notes Tables

Schedule of Long-Term Debt Instruments [Table Text Block]

	2024			2023
Spire
3.54% Senior Notes, due February 27, 2024	$	—			150.0
0.75% Remarketable Senior Notes, due March 1, 2026		—			175.0
5.30% Senior Notes, due March 1, 2026		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)		1,818.0			1,798.0
Total principal of Spire Alabama long-term debt (see below)		750.0			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		111.1			117.7
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		3,771.1			3,732.7
Less: Unamortized discounts and debt issuance costs		(24.7	)		(22.1	)
Less: Current portion		(42.0	)		(156.6	)
Long-term debt, excluding current portion	$	3,704.4		$	3,554.0
Spire Missouri
First Mortgage Bonds:
Floating Rate Series, due December 2, 2024	$	—			300.0
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
7.90% Series, due September 15, 2030		30.0			30.0
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			—
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		1,818.0			1,798.0
Less: Unamortized discounts and debt issuance costs		(14.6	)		(12.6	)
Spire Missouri long-term debt, excluding current portion	$	1,803.4		$	1,785.4
Spire Alabama
3.21% Notes, due September 15, 2025	$	35.0		$	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		750.0			750.0
Less: Unamortized discounts and debt issuance costs		(3.7	)		(4.1	)
Less: Current portion		(35.0	)		—
Spire Alabama long-term debt, excluding current portion	$	711.3		$	745.9

Schedule of Maturities of Long-Term Debt [Table Text Block]

	2025		2026		2027		2028		2029
Spire	$	42.0	$	487.5	$	108.1	$	53.6	$	28.5
Spire Missouri		—		—		—		45.0		19.3
Spire Alabama		35.0		—		—		—		—