Consolidated Balance Sheets - USD ($) $ in Millions		Sep. 30, 2023	Sep. 30, 2022
ASSETS
Utility Plant		$ 8,210.1	$ 7,664.9
Less: Accumulated depreciation and amortization		2,431.2	2,294.5
Net Utility Plant		5,778.9	5,370.4
Non-utility Property (net of accumulated depreciation and amortization of $71.1 and $50.7 at September 30, 2023 and 2022, respectively)		628.5	491.4
Other Investments		102.6	87.8
Total Other Property and Investments		731.1	579.2
Other Property and Investments		731.1	579.2
Current Assets:
Cash and cash equivalents		5.6	6.5
Utility		192.4	210.8
Other		128.6	443.8
Allowance for credit losses		(32.5)	(31.9)
Delayed customer billings		22.0	21.3
Accounts receivable:
Utility		192.4	210.8
Other		128.6	443.8
Allowance for credit losses		(32.5)	(31.9)
Delayed customer billings		22.0	21.3
Inventories:
Natural gas		223.7	371.8
Propane gas		8.6	8.6
Materials and supplies		47.2	41.9
Regulatory assets		348.3	355.4
Prepayments		48.2	41.1
Other current assets		84.8	122.7
Total Current Assets		1,076.9	1,592.0
Deferred Charges and Other Assets:
Goodwill		1,171.6	1,171.6
Regulatory assets		1,249.2	1,112.4
Other		305.9	258.1
Total Deferred Charges and Other Assets		2,726.7	2,542.1
Total Assets		10,313.6	10,083.7
Capitalization:
Common stock value		53.2	52.5
Paid-in capital		1,616.5	1,571.3
Retained earnings		958.0	905.5
Accumulated other comprehensive income		47.6	47.2
Total Shareholders' Equity		2,917.3	2,818.5
Temporary equity		16.5	13.1
Long-term debt (less current portion)		3,554.0	2,958.5
Total Capitalization		6,487.8	5,790.1
Current Liabilities:
Current portion of long-term debt		156.6	281.2
Notes payable		955.5	1,037.5
Accounts payable		253.1	617.4
Advance customer billings		20.9	18.7
Wages and compensation accrued		47.0	50.2
Customer deposits		27.7	28.2
Taxes accrued		104.1	90.1
Regulatory liabilities		7.3	3.7
Other current liabilities		183.2	226.6
Total Current Liabilities		1,755.4	2,353.6
Deferred Credits and Other Liabilities:
Deferred income taxes		743.7	675.1
Pension and postretirement benefit costs		137.3	163.0
Asset retirement obligations		577.4	520.9
Regulatory liabilities		472.4	418.2
Other noncurrent liabilities		139.6	162.8
Total Deferred Credits and Other Liabilities		2,070.4	1,940.0
Commitments and Contingencies (Note 16)
Total Capitalization and Liabilities		10,313.6	10,083.7
Depositary Shares [Member]
Capitalization:
Preferred stock ($25.00 par value per share; 10.0 million depositary shares authorized, issued and outstanding at September 30, 2023 and 2022)		242.0	242.0
Spire Missouri [Member]
ASSETS
Utility Plant		4,964.9	4,550.4
Less: Accumulated depreciation and amortization		1,043.2	982.1
Net Utility Plant		3,921.7	3,568.3
Total Other Property and Investments		65.7	58.9
Other Property and Investments		65.7	58.9
Current Assets:
Cash and cash equivalents		0.8	0.0
Utility		142.6	131.5
Other		21.1	44.5
Allowance for credit losses		(26.2)	(24.9)
Delayed customer billings		17.9	16.1
Accounts receivable:
Utility		142.6	131.5
Other		21.1	44.5
Allowance for credit losses		(26.2)	(24.9)
Delayed customer billings		17.9	16.1
Inventories:
Natural gas		132.8	215.3
Propane gas		8.6	8.6
Materials and supplies		24.2	22.0
Regulatory assets		293.1	288.1
Prepayments		26.7	23.3
Total Current Assets		642.9	728.2
Deferred Charges and Other Assets:
Goodwill		210.2	210.2
Regulatory assets		617.6	547.6
Other		147.4	105.0
Total Deferred Charges and Other Assets		975.2	862.8
Total Assets		5,605.5	5,218.2
Capitalization:
Common stock value		0.1	0.1
Paid-in capital		854.8	816.1
Retained earnings		992.4	931.9
Accumulated other comprehensive income		(2.5)	(2.7)
Total Shareholders' Equity	[1]	1,844.8	1,745.4
Long-term debt (less current portion)		1,785.4	1,387.7
Total Capitalization		3,630.2	3,133.1
Current Liabilities:
Current portion of long-term debt		0.0	250.0
Advance customer billings		11.0	7.0
Wages and compensation accrued		23.6	33.8
Customer deposits		5.8	6.5
Taxes accrued		60.3	50.4
Regulatory liabilities		0.0	0.0
Other current liabilities		48.7	45.6
Total Current Liabilities		786.3	970.9
Deferred Credits and Other Liabilities:
Deferred income taxes		531.8	500.1
Pension and postretirement benefit costs		103.3	115.5
Asset retirement obligations		111.1	110.6
Regulatory liabilities		389.4	331.8
Other noncurrent liabilities		53.4	56.2
Total Deferred Credits and Other Liabilities		1,189.0	1,114.2
Commitments and Contingencies (Note 16)
Total Capitalization and Liabilities		5,605.5	5,218.2
Spire Missouri [Member] | Related Party [Member]
Current Assets:
Utility		1.3	3.7
Accounts receivable:
Utility		1.3	3.7
Current Liabilities:
Notes payable		540.6	445.3
Accounts payable		10.5	13.3
Spire Missouri [Member] | Nonrelated Party [Member]
Current Liabilities:
Accounts payable		85.8	119.0
Spire Alabama Inc [Member]
ASSETS
Utility Plant		2,862.6	2,732.6
Less: Accumulated depreciation and amortization		1,273.0	1,184.1
Net Utility Plant		1,589.6	1,548.5
Current Assets:
Cash and cash equivalents		1.2	2.4
Utility		42.2	69.9
Other		6.6	6.5
Allowance for credit losses		(5.7)	(6.3)
Delayed customer billings		3.6	4.8
Accounts receivable:
Utility		42.2	69.9
Other		6.6	6.5
Allowance for credit losses		(5.7)	(6.3)
Delayed customer billings		3.6	4.8
Inventories:
Natural gas		52.4	72.5
Materials and supplies		19.1	16.3
Regulatory assets		41.6	56.9
Prepayments		6.4	5.8
Total Current Assets		168.6	230.1
Deferred Charges and Other Assets:
Regulatory assets		606.9	538.2
Other		84.2	81.3
Total Deferred Charges and Other Assets		691.1	630.5
Total Assets		2,449.3	2,409.1
Deferred income tax		0.0	11.0
Capitalization:
Retained earnings		642.1	589.1
Total Shareholders' Equity		928.0	906.0
Long-term debt (less current portion)		745.9	571.5
Total Capitalization		1,673.9	1,477.5
Common stock and paid-in capital (par value $0.01 per share; 3,000,000 shares authorized; 1,972,052 issued and outstanding at September 30, 2023 and 2022)		285.9	316.9
Current Liabilities:
Accounts payable		28.4	85.6
Advance customer billings		8.1	9.9
Wages and compensation accrued		6.6	7.6
Customer deposits		19.3	19.0
Taxes accrued		34.5	31.3
Regulatory liabilities		0.0	0.0
Other current liabilities		14.7	22.4
Total Current Liabilities		240.3	441.1
Deferred Credits and Other Liabilities:
Deferred income taxes		9.1	0.0
Pension and postretirement benefit costs		27.2	40.5
Asset retirement obligations		451.0	398.7
Regulatory liabilities		21.2	23.0
Other noncurrent liabilities		26.6	28.3
Total Deferred Credits and Other Liabilities		535.1	490.5
Commitments and Contingencies (Note 16)
Total Capitalization and Liabilities		2,449.3	2,409.1
Spire Alabama Inc [Member] | Related Party [Member]
Current Assets:
Utility		1.2	1.3
Accounts receivable:
Utility		1.2	1.3
Current Liabilities:
Notes payable		124.1	260.9
Accounts payable		$ 4.6	$ 4.4

[1] Accumulated other comprehensive income (loss)