Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Millions		Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022
ASSETS
Utility Plant		$ 8,345.0	$ 8,210.1	$ 7,769.4
Less: Accumulated depreciation and amortization		2,467.3	2,431.2	2,326.5
Net Utility Plant		5,877.7	5,778.9	5,442.9
Non-utility Property (net of accumulated depreciation and amortization of $76.5, $71.1 and $55.6 at December 31, 2023, September 30, 2023, and December 31, 2022, respectively)		687.1	628.5	508.9
Other Investments		105.5	102.6	93.5
Total Other Property and Investments		792.6	731.1	602.4
Other Property and Investments		792.6	731.1	602.4
Current Assets:
Cash and cash equivalents		4.8	5.6	4.8
Utility		428.8	192.4	479.4
Other		150.6	128.6	334.7
Allowance for credit losses		(35.4)	(32.5)	(34.5)
Delayed customer billings		22.0	22.0	26.7
Accounts receivable:
Utility		428.8	192.4	479.4
Other		150.6	128.6	334.7
Allowance for credit losses		(35.4)	(32.5)	(34.5)
Delayed customer billings		22.0	22.0	26.7
Inventories:
Natural gas		220.6	223.7	320.0
Propane gas		8.6	8.6	8.6
Materials and supplies		47.4	47.2	44.1
Regulatory assets		256.4	348.3	269.1
Prepayments		43.3	48.2	31.6
Other current assets		72.8	84.8	145.2
Total Current Assets		1,219.9	1,076.9	1,629.7
Deferred Charges and Other Assets:
Goodwill		1,171.6	1,171.6	1,171.6
Regulatory assets		1,266.9	1,249.2	1,220.7
Other		303.0	305.9	260.4
Total Deferred Charges and Other Assets		2,741.5	2,726.7	2,652.7
Total Assets		10,631.7	10,313.6	10,327.7
Capitalization:
Preferred stock ($25.00 par value per share; 10.0 million depositary shares authorized, issued and outstanding at December 31, 2023, September 30, 2023, and December 31, 2022)		242.0	242.0	242.0
Common stock (par value $1.00 per share; 70.0 million shares authorized; 55.0 million, 53.2 million, and 52.5 million shares issued and outstanding at December 31, 2023, September 30, 2023, and December 31, 2022, respectively)		55.0	53.2	52.5
Paid-in capital		1,727.4	1,616.5	1,571.8
Retained earnings		997.3	958.0	953.0
Accumulated other comprehensive income		29.1	47.6	44.8
Total Shareholders' Equity		3,050.8	2,917.3	2,864.1
Temporary equity		14.8	16.5	16.2
Long-term debt (less current portion)		3,247.8	3,554.0	3,156.3
Total Capitalization		6,313.4	6,487.8	6,036.6
Current Liabilities:
Current portion of long-term debt		457.0	156.6	256.6
Notes payable		1,047.5	955.5	1,227.0
Accounts payable		293.8	253.1	506.8
Advance customer billings		25.0	20.9	16.9
Wages and compensation accrued		26.1	47.0	30.6
Customer deposits		28.8	27.7	28.8
Taxes accrued		64.9	104.1	57.6
Regulatory liabilities		7.1	7.3	3.7
Other current liabilities		260.3	183.2	276.7
Total Current Liabilities		2,210.5	1,755.4	2,404.7
Deferred Credits and Other Liabilities:
Deferred income taxes		760.6	743.7	699.4
Pension and postretirement benefit costs		135.5	137.3	159.3
Asset retirement obligations		583.6	577.4	526.2
Regulatory liabilities		487.2	472.4	344.9
Other noncurrent liabilities		140.9	139.6	156.6
Total Deferred Credits and Other Liabilities		2,107.8	2,070.4	1,886.4
Total Capitalization and Liabilities		10,631.7	10,313.6	10,327.7
Spire Missouri [Member]
ASSETS
Utility Plant		5,080.2	4,964.9	4,632.6
Less: Accumulated depreciation and amortization		1,063.7	1,043.2	1,003.4
Net Utility Plant		4,016.5	3,921.7	3,629.2
Total Other Property and Investments		67.9	65.7	66.5
Other Property and Investments		67.9	65.7	66.5
Current Assets:
Cash and cash equivalents		0.0	0.8	0.0
Other		22.2	21.1	28.6
Allowance for credit losses		(28.9)	(26.2)	(28.2)
Delayed customer billings		16.8	17.9	21.5
Accounts receivable:
Other		22.2	21.1	28.6
Allowance for credit losses		(28.9)	(26.2)	(28.2)
Delayed customer billings		16.8	17.9	21.5
Inventories:
Natural gas		141.8	132.8	189.9
Propane gas		8.6	8.6	8.6
Materials and supplies		24.6	24.2	23.0
Regulatory assets		212.9	293.1	191.2
Prepayments		22.8	26.7	15.8
Total Current Assets		757.4	642.9	813.4
Deferred Charges and Other Assets:
Goodwill		210.2	210.2	210.2
Regulatory assets		630.8	617.6	634.7
Other		146.0	147.4	106.0
Total Deferred Charges and Other Assets		987.0	975.2	950.9
Total Assets		5,828.8	5,605.5	5,460.0
Capitalization:
Retained earnings		1,049.4	992.4	979.2
Accumulated other comprehensive income		(2.4)	(2.5)	(2.6)
Total Shareholders' Equity	[1]	1,901.9	1,844.8	1,792.8
Long-term debt (less current portion)		1,485.8	1,785.4	1,388.1
Total Capitalization		3,387.7	3,630.2	3,180.9
Paid-in capital and common stock		854.9	854.9	816.2
Current Liabilities:
Current portion of long-term debt		300.0	0.0	250.0
Advance customer billings		14.3	11.0	5.3
Wages and compensation accrued		14.4	23.6	21.5
Customer deposits		5.9	5.8	6.3
Taxes accrued		26.4	60.3	24.3
Other current liabilities		111.1	48.7	92.9
Total Current Liabilities		1,218.4	786.3	1,238.2
Deferred Credits and Other Liabilities:
Deferred income taxes		545.8	531.8	512.4
Pension and postretirement benefit costs		102.0	103.3	101.9
Asset retirement obligations		112.2	111.1	111.7
Regulatory liabilities		404.5	389.4	259.0
Other noncurrent liabilities		58.2	53.4	55.9
Total Deferred Credits and Other Liabilities		1,222.7	1,189.0	1,040.9
Commitments and Contingencies (Note 11)
Total Capitalization and Liabilities		5,828.8	5,605.5	5,460.0
Spire Missouri [Member] | Nonrelated Party [Member]
Current Assets:
Utility		335.5	142.6	357.2
Accounts receivable:
Utility		335.5	142.6	357.2
Current Liabilities:
Accounts payable		106.6	85.8	166.6
Spire Missouri [Member] | Related Party [Member]
Current Assets:
Utility		1.1	1.3	5.8
Accounts receivable:
Utility		1.1	1.3	5.8
Current Liabilities:
Notes payable		633.3	540.6	651.2
Accounts payable		6.4	10.5	20.1
Spire Alabama Inc [Member]
ASSETS
Utility Plant		2,879.8	2,862.6	2,755.8
Less: Accumulated depreciation and amortization		1,289.1	1,273.0	1,196.5
Net Utility Plant		1,590.7	1,589.6	1,559.3
Current Assets:
Cash and cash equivalents		0.0	1.2	0.0
Other		5.7	6.6	5.4
Allowance for credit losses		(5.7)	(5.7)	(5.5)
Delayed customer billings		4.6	3.6	4.8
Accounts receivable:
Other		5.7	6.6	5.4
Allowance for credit losses		(5.7)	(5.7)	(5.5)
Delayed customer billings		4.6	3.6	4.8
Inventories:
Natural gas		40.7	52.4	66.1
Materials and supplies		18.9	19.1	17.2
Regulatory assets		31.0	41.6	67.3
Prepayments		6.8	6.4	4.1
Total Current Assets		175.8	168.6	260.4
Deferred Charges and Other Assets:
Regulatory assets		612.6	606.9	560.4
Other		84.2	84.2	81.7
Total Deferred Charges and Other Assets		696.8	691.1	649.9
Total Assets		2,463.3	2,449.3	2,469.6
Deferred income taxes		0.0	0.0	7.8
Capitalization:
Retained earnings		639.2	642.1	595.3
Total Shareholders' Equity		924.1	928.0	900.7
Long-term debt (less current portion)		746.0	745.9	745.6
Total Capitalization		1,670.1	1,673.9	1,646.3
Paid-in capital and common stock		284.9	285.9	305.4
Current Liabilities:
Advance customer billings		8.8	8.1	9.7
Wages and compensation accrued		3.6	6.6	3.2
Customer deposits		20.0	19.3	19.7
Taxes accrued		32.6	34.5	28.8
Other current liabilities		18.2	14.7	20.7
Total Current Liabilities		249.9	240.3	319.0
Deferred Credits and Other Liabilities:
Deferred income taxes		13.0	9.1	0.0
Pension and postretirement benefit costs		26.5	27.2	51.4
Asset retirement obligations		455.8	451.0	402.8
Regulatory liabilities		20.7	21.2	22.2
Other noncurrent liabilities		27.3	26.6	27.9
Total Deferred Credits and Other Liabilities		543.3	535.1	504.3
Commitments and Contingencies (Note 11)
Total Capitalization and Liabilities		2,463.3	2,449.3	2,469.6
Spire Alabama Inc [Member] | Nonrelated Party [Member]
Current Assets:
Utility		73.7	42.2	100.2
Accounts receivable:
Utility		73.7	42.2	100.2
Current Liabilities:
Accounts payable		33.7	28.4	87.1
Spire Alabama Inc [Member] | Related Party [Member]
Current Assets:
Utility		0.1	1.2	0.8
Accounts receivable:
Utility		0.1	1.2	0.8
Current Liabilities:
Notes payable		128.5	124.1	145.8
Accounts payable		$ 4.5	$ 4.6	$ 4.0

[1] Accumulated other comprehensive income (loss)