Regulatory Matters (Tables)

12 Months Ended

Sep. 30, 2025

Regulated Operations [Abstract]

Schedule of Regulatory Assets and Liabilities

The following regulatory assets and regulatory liabilities were reflected in the balance sheets of the Company, Spire Missouri and Spire Alabama as of September 30, 2025 and 2024.

	Spire				Spire Missouri				Spire Alabama
September 30	2025		2024		2025		2024		2025		2024
Regulatory Assets:
Current:
Unamortized purchased gas adjustments	$	16.5	$	28.9	$	14.9	$	28.1	$	—	$	—
Other		61.8		86.5		34.0		55.9		16.1		19.2
Total Current Regulatory Assets		78.3		115.4		48.9		84.0		16.1		19.2
Noncurrent:
Future income taxes due from customers		154.2		150.7		146.6		142.7		1.6		1.8
Pension and postretirement benefit costs		217.8		237.5		157.0		166.5		59.1		68.2
Cost of removal		688.3		668.2		98.8		97.0		589.6		571.2
Unamortized purchased gas adjustments		9.0		1.2		9.0		1.2		—		—
Energy efficiency		65.0		61.0		65.0		61.0		—		—
Other		189.2		133.2		176.8		119.6		0.3		0.8
Total Noncurrent Regulatory Assets		1,323.5		1,251.8		653.2		588.0		650.6		642.0
Total Regulatory Assets	$	1,401.8	$	1,367.2	$	702.1	$	672.0	$	666.7	$	661.2
Regulatory Liabilities:
Current:
Unamortized purchased gas adjustments	$	34.9	$	42.3	$	13.9	$	10.2	$	20.2	$	30.9
Other		4.5		7.2		—		—		0.1		2.9
Total Current Regulatory Liabilities		39.4		49.5		13.9		10.2		20.3		33.8
Noncurrent:
Deferred taxes due to customers		100.3		114.2		88.8		101.8		—		—
Pension and postretirement benefit costs		300.1		232.9		261.2		196.6		26.5		25.1
Accrued cost of removal		138.2		133.6		96.0		94.5		—		—
Unamortized purchased gas adjustments		6.5		17.2		6.5		17.2		—		—
Other		32.9		37.6		28.8		33.2		2.7		3.2
Total Noncurrent Regulatory Liabilities		578.0		535.5		481.3		443.3		29.2		28.3
Total Regulatory Liabilities	$	617.4	$	585.0	$	495.2	$	453.5	$	49.5	$	62.1

Schedule of Regulatory Assets Not Earning Return

A portion of the Company’s and Spire Missouri's regulatory assets are not earning a return, as shown in the table below:

	Spire				Spire Missouri
September 30	2025		2024		2025		2024
Pension and postretirement benefit costs	$	119.1	$	129.7	$	119.1	$	129.7
Future income taxes due from customers		152.7		148.9		146.6		142.7
Unamortized purchase gas adjustments		23.9		29.3		23.9		29.3
Other		177.0		132.5		177.0		132.5
Total Regulatory Assets Not Earning a Return	$	472.7	$	440.4	$	466.6	$	434.2