Spire (SR) 10-K 18 Nov 20 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Sep. 30, 2020	Nov. 13, 2020	Mar. 31, 2020
Entity Information [Line Items]
Entity Registrant Name	Spire Inc
Entity Central Index Key	0001126956
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 3,703,018,742
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		51,618,125
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	false
Entity File Number	1-16681
Entity Tax Identification Number	74-2976504
Entity Address, Address Line One	700 Market Street
Entity Address, City or Town	St. Louis
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	63101
City Area Code	314
Local Phone Number	342-0500
Entity Incorporation, State or Country Code	MO
Document Annual Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Documents Incorporated by Reference	Portions of proxy statement for Spire Inc. to be filed on or about December 16, 2020 — Part III. Certain exhibits as indicated in Part IV.
Common Stock $1.00 par value
Entity Information [Line Items]
Trading Symbol	SR
Title of each class	Common Stock $1.00 par value
Name of each exchange on which registered	NYSE
Depositary Shares, each representing a 1/1,000th interest in a share of 5.90% Series A Cumulative Redeemable Perpetual Preferred Stock, par value $25.00 per share
Entity Information [Line Items]
Trading Symbol	SR.PRA
Title of each class	Depositary Shares
Name of each exchange on which registered	NYSE
Spire Missouri Inc
Entity Information [Line Items]
Entity Registrant Name	Spire Missouri Inc
Entity Central Index Key	0000057183
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Public Float			0
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		24,577
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	false
Entity File Number	1-1822
Entity Tax Identification Number	43-0368139
Entity Address, Address Line One	700 Market Street
Entity Address, City or Town	St. Louis
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	63101
City Area Code	314
Local Phone Number	342-0500
Entity Incorporation, State or Country Code	MO
Entity Interactive Data Current	Yes
Spire Alabama Inc
Entity Information [Line Items]
Entity Registrant Name	Spire Alabama Inc
Entity Central Index Key	0000003146
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Public Float			$ 0
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		1,972,052
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	false
Entity File Number	2-38960
Entity Tax Identification Number	63-0022000
Entity Address, Address Line One	605 Richard Arrington Blvd N
Entity Address, City or Town	Birmingham
Entity Address, State or Province	AL
Entity Address, Postal Zip Code	35203
City Area Code	205
Local Phone Number	326-8100
Entity Incorporation, State or Country Code	AL
Entity Interactive Data Current	Yes

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Operating Revenues	$ 1,855.4	$ 1,952.4	$ 1,965
Operating Expenses:
Natural gas	696.1	840.3	871.7
Operation and maintenance	458.6	474.1	477.3
Depreciation and amortization	197.3	181.7	168.4
Taxes, other than income taxes	148.4	154	153.5
Impairments	148.6	0	0
Total Operating Expenses	1,649	1,650.1	1,670.9
Operating Income	206.4	302.3	294.1
Interest Expense, Net	105.5	104.4	98.4
Other Income (Expense), Net	0.1	21.2	(8)
Income Before Income Taxes	101	219.1	187.7
Income Tax Expense (Benefit)	12.4	34.5	(26.5)
Net Income	88.6	184.6	214.2
Provision for preferred dividends	14.8	5.3
Income allocated to participating securities	0.1	0.4	0.5
Net Income Available to Common Shareholders	$ 73.7	$ 178.9	$ 213.7
Weighted Average Number of Common Shares Outstanding:
Basic	51.2	50.7	49.1
Diluted	51.3	50.8	49.3
Basic Earnings Per Share of Common Stock	$ 1.44	$ 3.53	$ 4.35
Diluted Earnings Per Share of Common Stock	$ 1.44	$ 3.52	$ 4.33
Spire Alabama
Operating Revenues	$ 455	$ 465.5	$ 500.7
Operating Expenses:
Natural gas	118.9	135.5	176
Operation and maintenance	139.1	142.6	138.8
Depreciation and amortization	59.3	56.2	53.2
Taxes, other than income taxes	34.8	35.7	36.1
Total Operating Expenses	352.1	370	404.1
Operating Income	102.9	95.5	96.6
Interest Expense, Net	20.6	21.7	17.3
Other Income (Expense), Net	5.4	7	3.6
Income Before Income Taxes	87.7	80.8	82.9
Income Tax Expense (Benefit)	22	20.5	81.6
Net Income	$ 65.7	$ 60.3	$ 1.3

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Net Income	$ 88.6	$ 184.6	$ 214.2
Cash flow hedging derivative instruments:
Net hedging (loss) gain arising during the period	(8.9)	(46.4)	3.9
Amounts reclassified into net income	(3.2)	(1.3)	(1.5)
Net (loss) gain on cash flow hedging derivative instruments	(12.1)	(47.7)	2.4
Defined benefit pension and other postretirement benefit plans:
Amortization of actuarial (gain) loss included in net periodic pension and postretirement benefit cost	(0.5)	(0.9)	0.4
Net defined benefit pension and other postretirement benefit plans	(0.5)	(0.9)	0.4
Net unrealized gain on available-for-sale debt securities		0.1	0.3
Other Comprehensive (Loss) Income, Before Tax	(12.6)	(48.5)	3.1
Income Tax (Benefit) Expense Related to Items of Other Comprehensive (Loss) Income	(2.7)	(10.8)	0.6
Other Comprehensive (Loss) Income, Net of Tax	(9.9)	(37.7)	2.5
Comprehensive Income	78.7	146.9	216.7
Operating Revenues	1,855.4	1,952.4	1,965
Operating Expenses:
Natural gas	696.1	840.3	871.7
Operation and maintenance	458.6	474.1	477.3
Depreciation and amortization	197.3	181.7	168.4
Taxes, other than income taxes	148.4	154	153.5
Total Operating Expenses	1,649	1,650.1	1,670.9
Operating Income	206.4	302.3	294.1
Interest Expense, Net	105.5	104.4	98.4
Other (Expense) Income, Net	0.1	21.2	(8)
Income Before Income Taxes	101	219.1	187.7
Income Tax Expense (Benefit)	12.4	34.5	(26.5)
Net Income	88.6	184.6	214.2
Spire Missouri
Net Income	130.2	115	129.3
Defined benefit pension and other postretirement benefit plans:
Other Comprehensive (Loss) Income, Net of Tax	(0.5)	(0.8)	0.4
Comprehensive Income	129.7	114.2	129.7
Operating Revenues	1,193.6	1,291.8	1,285.6
Operating Expenses:
Natural gas	515.8	629.8	636.8
Operation and maintenance	251	268.1	279.1
Depreciation and amortization	118	111.5	102.8
Taxes, other than income taxes	103.2	107.6	108.4
Total Operating Expenses	988	1,117	1,127.1
Operating Income	205.6	174.8	158.5
Interest Expense, Net	49.4	49.2	46.4
Other (Expense) Income, Net	(8.7)	2.7	(15.4)
Income Before Income Taxes	147.5	128.3	96.7
Income Tax Expense (Benefit)	17.3	13.3	(32.6)
Net Income	$ 130.2	$ 115	$ 129.3

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
ASSETS
Utility Plant	$ 6,766.3	$ 6,146.5
Less: Accumulated depreciation and amortization	2,086.2	1,794.5
Net Utility Plant	4,680.1	4,352
Non-utility Property (net of accumulated depreciation and amortization of $19.0 and $12.7 at September 30, 2020 and 2019, respectively)	432.3	477.8
Other Investments	71.7	72.3
Total Other Property and Investments	504	550.1
Current Assets:
Cash and cash equivalents	4.1	5.8
Accounts receivable:
Utility	131.8	139.8
Other	146.4	172.8
Allowance for doubtful accounts	(24.9)	(23)
Delayed customer billings	10	4.3
Inventories:
Natural gas	154.3	162.6
Propane gas	10.7	10.7
Materials and supplies	26.5	23.3
Regulatory assets	69.5	78.6
Prepayments	29.2	29.1
Other	33	10.5
Total Current Assets	590.6	614.5
Deferred Charges and Other Assets:
Goodwill	1,171.6	1,171.6
Regulatory assets	1,069.4	767.6
Other	225.5	163.4
Total Deferred Charges and Other Assets	2,466.5	2,102.6
Total Assets	8,241.2	7,619.2
Capitalization:
Preferred stock ($25.00 par value per share; 10.0 million depositary shares authorized, issued and outstanding at September 30, 2020 and 2019)	242	242
Common stock (par value $1.00 per share; 70.0 million shares authorized; 51.6 million issued and outstanding at September 30, 2020, and 51.0 million shares issued and outstanding September 30, 2019)	51.6	51
Paid-in capital and common stock	1,549.2	1,505.8
Retained earnings	720.7	775.5
Accumulated other comprehensive loss	(41.2)	(31.3)
Total Shareholders' Equity	2,522.3	2,543
Temporary equity	3.4	3.4
Long-term debt (less current portion)	2,423.7	2,082.6
Total Capitalization	4,949.4	4,629
Current Liabilities:
Current portion of long-term debt	60.4	40
Notes payable	648	743.2
Accounts payable	243.3	301.5
Advance customer billings	45.3	32.6
Wages and compensation accrued	46.3	45.7
Customer deposits	30.6	35.6
Taxes accrued	71.4	68.5
Regulatory liabilities	113	60.8
Other	190.9	140.9
Total Current Liabilities	1,449.2	1,468.8
Deferred Credits and Other Liabilities:
Deferred income taxes	511.4	451.4
Pension and postretirement benefit costs	309	264.8
Asset retirement obligations	540.1	337.6
Regulatory liabilities	343.7	399
Other	138.4	68.6
Total Deferred Credits and Other Liabilities	1,842.6	1,521.4
Commitments and Contingencies (Note 16)
Total Capitalization and Liabilities	8,241.2	7,619.2
Spire Missouri
ASSETS
Utility Plant	3,931.2	3,643.2
Less: Accumulated depreciation and amortization	825.7	764.1
Net Utility Plant	3,105.5	2,879.1
Other Investments	56.7	53.3
Current Assets:
Cash and cash equivalents	0	2.6
Accounts receivable:
Utility	92.5	94.6
Associated companies	2.7	1.4
Other	34.1	26.5
Allowance for doubtful accounts	(18.1)	(14.9)
Delayed customer billings	2.4	4.3
Inventories:
Natural gas	95.1	100.1
Propane gas	10.7	10.7
Materials and supplies	15.6	13.3
Regulatory assets	32.1	29.4
Prepayments	20.7	18.2
Total Current Assets	287.8	286.2
Deferred Charges and Other Assets:
Goodwill	210.2	210.2
Regulatory assets	548.7	507.5
Other	96	85.6
Total Deferred Charges and Other Assets	854.9	803.3
Total Assets	4,304.9	4,021.9
Capitalization:
Common stock (par value $1.00 per share; 70.0 million shares authorized; 51.6 million issued and outstanding at September 30, 2020, and 51.0 million shares issued and outstanding September 30, 2019)	0.1	0.1
Paid-in capital and common stock	765	765
Retained earnings	672.9	576.6
Accumulated other comprehensive loss	(2.9)	(2.4)
Total Shareholders' Equity	1,435.1	1,339.3
Long-term debt (less current portion)	1,092	925
Total Capitalization	2,527.1	2,264.3
Current Liabilities:
Notes payable – associated companies	301.2	386.4
Accounts payable	66.7	75.7
Accounts payable – associated companies	9.3	5.5
Advance customer billings	32.7	20.8
Wages and compensation accrued	33.3	34.5
Customer deposits	9.3	13.4
Taxes accrued	39.1	36.4
Regulatory liabilities	103.2	52.3
Other	39.9	26.4
Total Current Liabilities	634.7	651.4
Deferred Credits and Other Liabilities:
Deferred income taxes	434.7	364.6
Pension and postretirement benefit costs	217.2	192.4
Asset retirement obligations	153.4	173.5
Regulatory liabilities	274.8	326.5
Other	63	49.2
Total Deferred Credits and Other Liabilities	1,143.1	1,106.2
Commitments and Contingencies (Note 16)
Total Capitalization and Liabilities	4,304.9	4,021.9
Spire Alabama
ASSETS
Utility Plant	2,469.9	2,138
Less: Accumulated depreciation and amortization	1,117	882.1
Net Utility Plant	1,352.9	1,255.9
Accounts receivable:
Utility	31.4	37.5
Associated companies	0.6	0
Other	5.8	8.5
Allowance for doubtful accounts	(5.5)	(6.3)
Delayed customer billings	7.5	0
Inventories:
Natural gas	22.5	35.1
Materials and supplies	8.4	7.8
Regulatory assets	20.4	33.9
Prepayments	4.3	5.3
Other	0.2	0.4
Total Current Assets	95.6	122.2
Deferred Charges and Other Assets:
Regulatory assets	489.9	231.2
Deferred income taxes	59.3	81.3
Other	53.7	53
Total Deferred Charges and Other Assets	602.9	365.5
Total Assets	2,051.4	1,743.6
Capitalization:
Paid-in capital and common stock	350.9	370.9
Retained earnings	500.8	459.1
Total Shareholders' Equity	851.7	830
Long-term debt (less current portion)	471.8	372.2
Total Capitalization	1,323.5	1,202.2
Current Liabilities:
Current portion of long-term debt	0	40
Notes payable – associated companies	121.3	128.7
Accounts payable	43.7	56.2
Accounts payable – associated companies	4.2	1.6
Advance customer billings	11.5	10.6
Wages and compensation accrued	8	8
Customer deposits	18.7	19.5
Taxes accrued	28	27.4
Regulatory liabilities	3.9	3.4
Other	11.8	9.2
Total Current Liabilities	251.1	304.6
Deferred Credits and Other Liabilities:
Pension and postretirement benefit costs	74.9	59.2
Asset retirement obligations	374.3	148.7
Regulatory liabilities	18.5	23
Other	9.1	5.9
Total Deferred Credits and Other Liabilities	476.8	236.8
Commitments and Contingencies (Note 16)
Total Capitalization and Liabilities	$ 2,051.4	$ 1,743.6

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
ASSETS
Non-utility property, accumulated depreciation and amortization	$ 19	$ 12.7
Capitalization:
Preferred stock, depositary shares authorized (in shares)	5,000,000	5,000,000
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, authorized (in shares)	70,000,000	70,000,000
Common stock, issued (in shares)	51,600,000	51,000,000
Common stock, outstanding (in shares)	51,600,000	51,000,000
Spire Missouri
Capitalization:
Preferred stock, depositary shares authorized (in shares)	1,480,000	1,480,000
Preferred stock, depositary shares outstanding (in shares)	0	0
Preferred stock, depositary shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, authorized (in shares)	50,000,000	50,000,000
Common stock, issued (in shares)	24,577	24,577
Common stock, outstanding (in shares)	24,577	24,577
Spire Alabama
Capitalization:
Preferred stock, depositary shares authorized (in shares)	120,000	120,000
Preferred stock, depositary shares outstanding (in shares)	0	0
Preferred stock, depositary shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized (in shares)	3,000,000	3,000,000
Common stock, issued (in shares)	1,972,052	1,972,052
Common stock, outstanding (in shares)	1,972,052	1,972,052
Depositary Shares
Capitalization:
Preferred stock, par value (in dollars per share)	$ 25	$ 25
Preferred stock, depositary shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, depositary shares outstanding (in shares)	10,000,000	10,000,000
Preferred stock, depositary shares issued (in shares)	10,000,000	10,000,000

CONSOLIDATED STATEMENTS OF SHAR

CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Millions	Total	Spire Missouri	Spire Alabama	Common Stock	Common StockSpire Missouri	Common StockSpire Alabama	Preferred Stock	Paid-in Capital	Paid-in CapitalSpire Missouri	Paid-in CapitalSpire Alabama	Retained Earnings	Retained EarningsSpire Missouri	Retained EarningsSpire Alabama	AOCI	[1]	AOCISpire Missouri	[1]
BALANCE at Sep. 30, 2017	$ 1,991.3	$ 1,171	$ 867.4	$ 48.3	$ 0.1			$ 1,325.6	$ 756.1	$ 420.9	$ 614.2	$ 416.5	$ 446.5	$ 3.2		$ (1.7)
BALANCE (in shares) at Sep. 30, 2017				48,263,243	24,577	1,972,052
Stockholders' Equity Rollforward
Net Income	214.2	129.3	1.3								214.2	129.3	1.3
Common stock issued	153			$ 2.3				150.7
Common stock issued (in shares)				2,300,000
Dividend reinvestment plan	1.6							1.6
Dividend reinvestment plan (in shares)				23,023
Stock-based compensation costs	7.7	4.2						7.7	4.2
Stock issued under stock-based compensation plans				$ 0.1				(0.1)
Stock issued under stock-based compensation plans (in shares)				119,592
Employees’ tax withholding for stock-based compensation	(2.8)							(2.8)
Employee's tax withholding for stock-based compensation (in shares)				(33,955)
Dividends declared on common stock	(112.1)	(45)	(30)								(112.1)	(45)	(30)
Other comprehensive income (loss), net of tax	2.5	0.4												2.5		0.4
Return of capital to Spire			(30)							(30)
Reclassification of certain income tax effects											(0.7)	0.3		0.7		(0.3)
BALANCE at Sep. 30, 2018	2,255.4	1,259.9	808.7	$ 50.7	$ 0.1			1,482.7	760.3	390.9	715.6	501.1	417.8	6.4		(1.6)
BALANCE (in shares) at Sep. 30, 2018				50,671,903	24,577	1,972,052
Stockholders' Equity Rollforward
Net Income	184.6	115	60.3								184.6	115	60.3
Common stock issued	14.4			$ 0.2				14.2
Common stock issued (in shares)				179,630
Dividend reinvestment plan	5.1							5.1
Dividend reinvestment plan (in shares)				62,735
Stock-based compensation costs	6.2	4.7						6.2	4.7
Stock issued under stock-based compensation plans				$ 0.1				(0.1)
Stock issued under stock-based compensation plans (in shares)				87,978
Employees’ tax withholding for stock-based compensation	(2.3)							(2.3)
Employee's tax withholding for stock-based compensation (in shares)				(28,731)
Temporary equity adjustment to redemption value	(0.8)										(0.8)
Preferred stock issued	242						$ 242
Dividends declared on common stock	(120.5)	(39.5)	(19)								(120.5)	(39.5)	(19)
Dividends declared on preferred stock	(3.4)										(3.4)
Other comprehensive income (loss), net of tax	(37.7)	(0.8)												(37.7)		(0.8)
Return of capital to Spire			(20)							(20)
BALANCE at Sep. 30, 2019	2,543	1,339.3	830	$ 51	$ 0.1		242	1,505.8	765	370.9	775.5	576.6	459.1	(31.3)		(2.4)
BALANCE (in shares) at Sep. 30, 2019				50,973,515	24,577	1,972,052
Stockholders' Equity Rollforward
Net Income	88.6	130.2	65.7								88.6	130.2	65.7
Common stock issued	32			$ 0.4				31.6
Common stock issued (in shares)				446,619
Dividend reinvestment plan	9.2			$ 0.1				9.1
Dividend reinvestment plan (in shares)				122,545
Stock-based compensation costs	6							6
Stock issued under stock-based compensation plans				$ 0.1				(0.1)
Stock issued under stock-based compensation plans (in shares)				110,463
Employees’ tax withholding for stock-based compensation	(3.2)							(3.2)
Employee's tax withholding for stock-based compensation (in shares)				(41,353)
Temporary equity adjustment to redemption value	3.4										3.4
Dividends declared on common stock	(128.4)	(33.9)	(24)								(128.4)	(33.9)	(24)
Dividends declared on preferred stock	(18.4)										(18.4)
Other comprehensive income (loss), net of tax	(9.9)	(0.5)												(9.9)		(0.5)
Return of capital to Spire			(20)							(20)
BALANCE at Sep. 30, 2020	$ 2,522.3	$ 1,435.1	$ 851.7	$ 51.6	$ 0.1		$ 242	$ 1,549.2	$ 765	$ 350.9	$ 720.7	$ 672.9	$ 500.8	$ (41.2)		$ (2.9)
BALANCE (in shares) at Sep. 30, 2020				51,611,789	24,577	1,972,052
[1]	Accumulated other comprehensive income (loss)

CONSOLIDATED STATEMENTS OF SH_2

CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Statement Of Stockholders Equity [Abstract]
Dividends declared on common stock (in dollars per share)	$ 2.49	$ 2.37	$ 2.25
Dividends declared on preferred stock (in dollars per depositary share)	$ 1.84375	$ 0.344

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Operating Activities:
Net Income	$ 88.6	$ 184.6	$ 214.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	197.3	181.7	168.4
Impairments	148.6	0	0
Deferred income taxes and investment tax credits	9	31.8	(28.7)
Changes in assets and liabilities:
Accounts receivable	36.2	2.7	(32.7)
Inventories	2.6	13.6	15.5
Regulatory assets and liabilities	0.6		191
Accounts payable	(43.1)	(6.4)	12.6
Delayed/advance customer billings, net	7	12.4	(12.8)
Taxes accrued	2.9	3.5	6.4
Other assets and liabilities	12	31	(121.2)
Other	8.2	(4)	43.9
Net cash provided by operating activities	469.9	450.9	456.6
Investing Activities:
Capital expenditures	(638.4)	(823.3)	(499.4)
Other business acquisitions		(7.9)	(28.1)
Other	6.8	(7.1)	(4.2)
Net cash used in investing activities	(631.6)	(838.3)	(531.7)
Financing Activities:
Issuance of preferred stock		242
Issuance of long-term debt	510	230	75
Repayment of long-term debt	(147)	(184.1)	(105)
(Repayment) issuance of short-term debt, net	(95.2)	189.6	76.3
Issuance of common stock	41.1	19.5	154.7
Dividends paid on common stock	(128)	(119)	(108.7)
Dividends paid on preferred stock	(14.8)	(3.4)
Other	(6.1)	(2.8)	(3.2)
Net cash provided by financing activities	160	371.8	89.1
Net (Decrease) Increase in Cash, Cash Equivalents, and Restricted Cash	(1.7)	(15.6)	14
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	5.8	21.4	7.4
Cash, Cash Equivalents, and Restricted Cash at End of Year	4.1	5.8	21.4
Supplemental disclosure of cash paid for:
Interest, net of amounts capitalized	(100)	(102.4)	(95.1)
Income taxes	(2.9)	(2.7)	(1.5)
Spire Missouri
Operating Activities:
Net Income	130.2	115	129.3
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	118	111.5	102.8
Deferred income taxes and investment tax credits	17.1	13.2	(32.6)
Changes in assets and liabilities:
Accounts receivable	(3.7)	(0.3)	(2)
Inventories	2.7	29	8.4
Regulatory assets and liabilities	27.3	32.7	141.5
Accounts payable	2.3	(8.4)	(14.8)
Delayed/advance customer billings, net	13.7	13.9	(7.4)
Taxes accrued	2.7	4.4	(2.1)
Other assets and liabilities	(6.1)	(2.6)	(83.9)
Other	0.6	5.2	45
Net cash provided by operating activities	304.8	313.6	284.2
Investing Activities:
Capital expenditures	(356)	(356.9)	(295.8)
Other	1.3	1.3	4.8
Net cash used in investing activities	(354.7)	(355.6)	(291)
Financing Activities:
Issuance of long-term debt	275	100
Repayment of long-term debt	(107)	(50)	(100)
(Repayments of) borrowings from Spire	(85.2)	41.1	142.3
Dividends paid on common stock	(33.9)	(48.5)	(36)
Other	(1.6)
Net cash provided by financing activities	47.3	42.6	6.3
Net (Decrease) Increase in Cash, Cash Equivalents, and Restricted Cash	(2.6)	0.6	(0.5)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	2.6	2	2.5
Cash, Cash Equivalents, and Restricted Cash at End of Year		2.6	2
Supplemental disclosure of cash paid for:
Interest, net of amounts capitalized	(46)	(48.7)	(45.6)
Income taxes	0	0	0
Spire Alabama
Operating Activities:
Net Income	65.7	60.3	1.3
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	59.3	56.2	53.2
Deferred income taxes and investment tax credits	22	20.5	81.6
Changes in assets and liabilities:
Accounts receivable	7.3	0.8	(16.2)
Inventories	11.9	(1.2)	(1.2)
Regulatory assets and liabilities	(23.5)	(28.2)	40.7
Accounts payable	(15.1)	4.5	4.7
Delayed/advance customer billings, net	(6.6)	(2.5)	(5.5)
Taxes accrued	0.6	(0.9)	4.9
Other assets and liabilities	18.9	34.8	(16.7)
Other	0.2	(3.2)	(0.7)
Net cash provided by operating activities	140.7	141.1	146.1
Investing Activities:
Capital expenditures	(150.4)	(174.5)	(131.7)
Other	1.6	(3.3)	(1.6)
Net cash used in investing activities	(148.8)	(177.8)	(133.3)
Financing Activities:
Issuance of long-term debt	100	90	75
Repayment of long-term debt	(40)	0	0
(Repayments of) borrowings from Spire	(7.4)	(13.8)	(27.4)
Return of capital to Spire	(20)	(20)	(30)
Dividends paid on common stock	(24)	(19)	(30)
Other	(0.5)	(0.5)	(0.5)
Net cash provided by financing activities	8.1	36.7	(12.9)
Net (Decrease) Increase in Cash, Cash Equivalents, and Restricted Cash	0	0	(0.1)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	0	0	0.1
Cash, Cash Equivalents, and Restricted Cash at End of Year	0	0	0
Supplemental disclosure of cash paid for:
Interest, net of amounts capitalized	(19)	(19.2)	(15.1)
Income taxes	$ 0	$ 0	$ 0

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES BASIS OF PRESENTATION – These notes are an integral part of the accompanying audited financial statements of Spire Inc. (“Spire” or the “Company”) presented on a consolidated basis, Spire Missouri Inc. (“Spire Missouri”) and Spire Alabama Inc. (“Spire Alabama”). Spire Missouri and Spire Alabama are wholly owned subsidiaries of Spire. Spire Missouri, Spire Alabama and the subsidiaries of Spire EnergySouth Inc. (“Spire EnergySouth”) are collectively referred to as the “Utilities.” The subsidiaries of Spire EnergySouth are Spire Gulf Inc. and Spire Mississippi Inc. Unless otherwise indicated, references to years herein are references to the fiscal years ending September 30 for the Company and its subsidiaries. The accompanying audited financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP). The consolidated financial position, results of operations and cash flows of Spire include the accounts of the Company and all its subsidiaries. Transactions and balances between consolidated entities have been eliminated from the consolidated financial statements of Spire. In compliance with GAAP, transactions between Spire Missouri and Spire Alabama and their affiliates, as well as intercompany balances on their balance sheets, have not been eliminated from their separate financial statements. NATURE OF OPERATIONS – Spire has two reportable segments: Gas Utility and Gas Marketing. The Gas Utility segment consists of the regulated natural gas distribution operations of the Company and is the core business segment of Spire in terms of revenue and earnings. The Gas Utility segment is comprised of the operations of: Spire Missouri, serving St. Louis, Kansas City, and other areas in Missouri; Spire Alabama, serving central and northern Alabama; and the subsidiaries of Spire EnergySouth, serving the Mobile, Alabama area and south-central Mississippi. The Gas Marketing segment includes Spire’s primary gas-related business, Spire Marketing Inc. (“Spire Marketing”), which provides non-regulated natural gas services, primarily in the central and southern United States (U.S.). The activities of other subsidiaries are reported as Other and are described in Note 14 , Information by Operating Segment. Spire Missouri and Spire Alabama each have a single reportable segment. USE OF ESTIMATES – The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates. SYSTEM OF ACCOUNTS – The accounts of the Utilities are maintained in accordance with the Uniform System of Accounts prescribed by the applicable state public service commissions, which systems substantially conform to that prescribed by the Federal Energy Regulatory Commission (FERC). PROPERTY, PLANT, AND EQUIPMENT – Utility Plant – Utility plant is stated at original cost. The cost of additions to utility plant includes contracted work, direct labor and materials, allocable overheads and an allowance for funds used during construction. The costs of units of property retired, replaced or renewed are removed from utility plant and are charged to accumulated depreciation. Maintenance and repairs of property and replacement and renewal of items determined to be less than units of property are charged to maintenance expenses. For Spire Missouri, utility plant is depreciated on a straight-line basis at rates based on estimated service lives of the various classes of property. In fiscal year 2020, the average depreciation and amortization expense averaged 2.9%, while in fiscal years 2019 and 2018, annual depreciation and amortization expense averaged 3.0% of the original cost of depreciable and amortizable property. For Spire Alabama, depreciation is provided using the composite method of depreciation on a straight-line basis over the estimated useful lives of utility property at rates approved by the Alabama Public Service Commission (APSC). The composite depreciation rate in fiscal years 2020, 2019 and 2018 was approximately 3.1%. Non-utility Property – Non-utility property is recorded at the original cost of acquisition or construction, which includes material, labor, contractor services and, for FERC-regulated projects, an allowance for funds used during construction. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Upon retirement or sale of non-utility property, the original cost and related accumulated depreciation are removed from the accounts and any gain or loss is included in the income statements. Costs related to software developed or obtained for internal use are capitalized and amortized on a straight-line basis over the estimated useful life of the related software. If software is retired prior to being fully amortized, the difference is recorded as a loss in the income statements. Accrued Capital Expenditures – Accrued capital expenditures, shown in the following table, are excluded from capital expenditures in the statements of cash flows until paid. September 30 2020 2019 2018 Spire $ 67.6 $ 80.6 $ 62.1 Spire Missouri 34.3 40.1 36.7 Spire Alabama 17.0 11.9 8.9 ASSET RETIREMENT OBLIGATIONS – Spire, Spire Missouri and Spire Alabama record legal obligations associated with the retirement of long-lived assets in the period in which the obligations are incurred, if sufficient information exists to reasonably estimate the fair value of the obligations. Obligations are recorded as both a cost of the related long-lived asset and as a corresponding liability. Subsequently, the asset retirement costs are depreciated over the life of the asset and the asset retirement obligations are accreted to the expected settlement amounts. The Company, Spire Missouri and Spire Alabama record asset retirement obligations associated with certain safety requirements to purge and seal gas distribution mains upon retirement, the plugging and abandonment of storage wells and other storage facilities, specific service line obligations, and certain removal and disposal obligations related to components of Spire Missouri’s, Spire Alabama’s and Spire Gulf’s distribution systems and general plant. Asset retirement obligations recorded by Spire’s other subsidiaries are not material. As authorized by the Missouri Public Service Commission (MoPSC) and APSC, Spire Missouri, Spire Alabama and Spire Gulf accrue future asset removal costs associated with their property, plant and equipment even if a legal obligation does not exist. Such accruals are provided for through depreciation expense and are recorded with corresponding credits to regulatory liabilities or regulatory assets. When those utilities retire depreciable utility plant and equipment, they charge the associated original costs to accumulated depreciation and amortization, and any related removal costs incurred are charged to regulatory liabilities or regulatory assets. The difference between removal costs recognized in depreciation rates and the accretion expense and depreciation expense recognized for financial reporting purposes is a timing difference between recovery of these costs in rates and their recognition for financial reporting purposes. Accordingly, these differences are deferred as regulatory liabilities or regulatory assets. In the rate setting process, the regulatory liabilities or regulatory assets are excluded from the rate base upon which those utilities have the opportunity to earn their allowed rates of return. In fiscal 2020, Spire Alabama refined certain assumptions and estimates used in calculating its asset retirement obligations, resulting in both an increase in cost to retire gas distribution assets and a change in the timing of the related cash outflows. As a result of this change in estimate, which the Company believes is more precise, Spire Alabama recorded a $221.1 increase to its asset retirement obligations. Related adjustments were made to regulatory assets and utility plant, with no impact on earnings. The following table presents a reconciliation of the beginning and ending balances of asset retirement obligations at September 30, as reported in the balance sheets. Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Asset retirement obligations, beginning of year $ 337.6 $ 321.1 $ 173.5 $ 174.1 $ 148.7 $ 135.7 Liabilities incurred during the period 3.0 10.8 2.6 1.6 — 8.8 Liabilities settled during the period (6.9 ) (8.3 ) (4.0 ) (6.8 ) (1.6 ) (0.8 ) Accretion 14.0 13.0 7.2 7.4 6.1 5.0 Revisions in estimated cash flows 192.4 1.0 (25.9 ) (2.8 ) 221.1 — Asset retirement obligations, end of year $ 540.1 $ 337.6 $ 153.4 $ 173.5 $ 374.3 $ 148.7 REGULATED OPERATIONS – The Utilities account for their regulated operations in accordance with Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC) Topic 980, Regulated Operations . This topic sets forth the application of GAAP for those companies whose rates are established by or are subject to approval by an independent third-party regulator. The provisions of this accounting guidance require, among other things, that financial statements of a regulated enterprise reflect the actions of regulators, where appropriate. These actions may result in the recognition of revenues and expenses in time periods that are different than non-regulated enterprises. When this occurs, costs are deferred as assets in the balance sheet (regulatory assets) and recorded as expenses when those amounts are reflected in rates. In addition, regulators can impose liabilities upon a regulated company for amounts previously collected from customers and for recovery of costs that are expected to be incurred in the future (regulatory liabilities). Management believes that the current regulatory environment supports the continued use of these regulatory accounting principles and that all regulatory assets and regulatory liabilities are recoverable or refundable through the regulatory process. See additional discussion on regulated operations in Note 15 , Regulatory Matters. NATURAL GAS AND PROPANE GAS – For Spire Missouri’s eastern region, inventory of natural gas in storage is priced on a last in, first out (LIFO) basis and inventory of propane gas in storage is priced on a first in, first out (FIFO) basis. For the rest of the Gas Utility segment, inventory of natural gas in storage is priced on the weighted average cost basis. The replacement cost of Spire Missouri’s natural gas for current use in eastern Missouri at September 30, 2020, and September 30, 2019, was less than the LIFO cost by $12.5 and $17.0, respectively. The carrying value of the Utilities’ inventory is never adjusted to a lower net realizable value or market value because, pursuant to Purchased Gas Adjustment (PGA) clauses or a Gas Supply Adjustment (GSA) rider, actual gas costs are recovered in customer rates. Natural gas and propane gas storage inventory in Spire’s other operating segments is recorded at the lower of average cost or net realizable value. BUSINESS COMBINATIONS – Spire’s acquisitions were accounted for using business combination accounting. Under this method, the purchase price paid by the acquirer is allocated to the assets acquired and liabilities assumed as of the acquisition date based on their fair value. In December 2017, the Company acquired an 80% voting interest in a natural gas storage facility in Wyoming. The transaction was valued at $24.8, consisting of $16.0 in cash and a $10.0 non-interest-bearing note valued at $8.8. In October 2018, the Company completed the exercise of its right to call the remaining 20% voting interest in that facility and settled the related note for a combined total of $17.0. In May 2018, the Company expanded its operations by acquiring 100% of a neighboring natural gas storage facility for $12.2 in cash. Together, these storage operations are referred to herein as “Spire Storage.” GOODWILL – Goodwill is measured as the excess of the acquisition-date fair value of the consideration transferred over the amount of acquisition-date identifiable assets acquired net of assumed liabilities. At September 30, 2020, goodwill included in Spire’s Gas Utility and Gas Marketing segments was $210.2 and zero, respectively, with the remainder held at the corporate level. Goodwill amounts have not changed since fiscal 2017, and there are no accumulated impairment losses. Spire and Spire Missouri evaluate goodwill for impairment as of July 1 of each year, or more frequently if events and circumstances indicate that goodwill might be impaired. At July 1, 2020 and 2019, Spire and Spire Missouri conducted qualitative assessments and determined goodwill was not impaired. The Company updated the assessments as of September 30, 2020, determining that it remained more likely than not that the fair value of each reporting unit exceeded its carrying value. IMPAIRMENT OF LONG-LIVED ASSETS – Long-lived assets classified as held and used are evaluated for impairment when events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. Whether impairment has occurred is determined by comparing the estimated undiscounted cash flows attributable to the assets with the carrying value of the assets. If the carrying value exceeds the undiscounted cash flows, the Company recognizes an impairment charge equal to the amount of the carrying value that exceeds the estimated fair value of the assets. In the period in which the Company determines an asset meets held-for-sale criteria, an impairment charge is recorded to the extent the book value exceeds its fair value less cost to sell. On July 1, 2020, Spire’s Board of Directors, based upon the recommendation of senior management, revised the development plan for Spire Storage, resulting in an impairment charge of $140.8 related to Spire Storage assets (non-utility property on the balance sheet) in the quarter ended June 30, 2020. The revision was driven by the realization that a longer time horizon will be required for optimization and positioning of the storage facility to serve energy markets in the western United States. Among other factors, evaluations of the continuing evolution of market dynamics in the region led management to update models of various development alternatives. Separately in the quarter ended June 30, 2020, Spire recorded impairment charges totaling $7.8 related to two commercial compressed natural gas fueling stations (also non-utility property) as a result of revised projections reflecting lower diesel prices and slower conversions of Class 8 vehicles. The fair values used in measuring the impairment charges were determined with an expected present value technique using a discounted cash flow method under an income approach. DERIVATIVES – In the course of their business, certain subsidiaries of Spire enter into commitments associated with the purchase or sale of natural gas. Certain of their derivative natural gas contracts are designated as normal purchases or normal sales and, as such, are excluded from the scope of FASB ASC Topic 815, Derivatives and Hedging . Those contracts are accounted for as executory contracts and recorded on an accrual basis. Revenues and expenses from such contracts are recorded gross. Contracts not designated as normal purchases or normal sales are recorded as derivatives with changes in fair value recognized in earnings in the periods prior to physical delivery. Certain of Spire Marketing’s wholesale purchase and sale transactions are classified as trading activities for financial reporting purposes. Under GAAP, revenues and expenses associated with trading activities are presented on a net basis in Gas Marketing operating revenues (or expenses, if negative) in the Condensed Consolidated Statements of Income. This net presentation has no effect on operating income or net income. Refer to Note 10 , Derivative Instruments and Hedging Activities, for more information about derivatives. INCOME TAXES – Spire and its subsidiaries account for income taxes under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amount of existing assets and liabilities and the respective tax basis and for tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be realized or settled. The effects on deferred tax assets and liabilities of a change in enacted tax rates is recognized in income or loss for non-regulated operations, and in a regulatory asset or regulatory liability for regulated operations. A valuation allowance is established when it is more likely than not that some portion or all of the deferred tax assets will not be realized. The Company accounts for uncertain tax positions in accordance with authoritative guidance. The authoritative guidance addresses the determination of whether tax benefits claimed, or expected to be claimed, on a tax return should be recorded in the financial statements. Spire may recognize the tax benefit from an uncertain tax position only if it is more likely than not that the position will be sustained upon examination by the taxing authority, based on the technical merits of the position. Tax-related interest and penalties, if any, are classified as a liability on the balance sheets. For additional information on the accounting for income taxes, refer to Note 12 , Income Taxes. CASH, CASH EQUIVALENTS, AND RESTRICTED CASH – All highly liquid debt instruments purchased with original maturities of three months or less are considered to be cash equivalents. Such instruments are carried at cost, which approximates market value. Outstanding checks on the Company’s and Utilities’ bank accounts in excess of funds on deposit create book overdrafts (which are funded at the time checks are presented for payment) and are classified as Other in the Current Liabilities section of the balance sheets. Changes in book overdrafts are reflected as Operating Activities in the statements of cash flows. In Spire’s statements of cash flows, total cash, cash equivalents, and restricted cash included $17.0 of restricted cash reported in “Other” current assets on Spire’s balance sheet as of September 30, 2018 (in addition to amounts shown as “Cash and cash equivalents”). This restricted cash was an escrow deposit for the purchase of the remaining 20% interest in a natural gas storage business and the settlement of the related note payable, and the transaction was completed on October 25, 2018. NATURAL GAS RECEIVABLE – Spire Marketing enters into natural gas transactions with natural gas pipeline and storage companies known as park and loan arrangements. Under the terms of the arrangements, Spire Marketing purchases natural gas from a third party and delivers that natural gas to the pipeline or storage company for the right to receive the same quantity of natural gas from that company at the same location in a future period. These arrangements are accounted for as non-monetary transactions under GAAP and are recorded at the carrying amount. As such, natural gas receivables are reflected on the Consolidated Balance Sheets at cost, which includes related fees associated with the transactions. In the period that the natural gas is returned to Spire Marketing, concurrent with the sale of the natural gas to a third party, the related natural gas receivable is expensed in the Consolidated Statements of Income. In conjunction with these transactions, Spire Marketing usually enters into New York Mercantile Exchange (NYMEX) and Intercontinental Exchange (ICE) natural gas futures, options, and swap contracts or fixed price sales agreements to protect against market changes in future sales prices. EARNINGS PER COMMON SHARE – GAAP requires dual presentation of basic and diluted earnings per share (EPS). EPS is computed using the two-class method, which is an earnings allocation method for computing EPS that treats a participating security as having rights to earnings that would otherwise have been available to common shareholders. Certain of the Company’s stock-based compensation awards pay non-forfeitable dividends to the participants during the vesting period and, as such, are deemed participating securities. Basic EPS is computed by dividing net income available to common shareholders by the weighted average number of common shares outstanding during the period. Diluted EPS is computed by dividing net income available to common shareholders by the weighted average number of common shares outstanding that are increased for additional shares that would be outstanding if potentially dilutive non-participating securities were converted to common shares, pursuant to the treasury stock method. Shares attributable to equity units, non-participating stock options and time-vested restricted stock/units are excluded from the calculation of diluted earnings per share if the effect would be antidilutive. Shares attributable to non-participating performance-contingent restricted stock awards are only included in the calculation of diluted earnings per share to the extent the underlying performance and/or market conditions are satisfied (a) prior to the end of the reporting period or (b) would be satisfied if the end of the reporting period were the end of the related contingency period and the result would be dilutive. The Company’s EPS computations are presented in Note 4 , Earnings Per Common Share. TRANSACTIONS WITH AFFILIATES – Transactions between affiliates of the Company have been eliminated from the consolidated financial statements of Spire. Spire Missouri and Spire Alabama borrowed funds from the Company and incurred related interest, as reflected in their separate financial statements, and they participated in normal intercompany shared services transactions. In addition, Spire Missouri’s other transactions with affiliates included: 2020 2019 2018 Purchases of natural gas from Spire Marketing $ 56.9 $ 95.3 $ 71.5 Sales of natural gas to Spire Marketing 0.1 1.7 0.3 Transportation services received from STL Pipeline LLC 27.9 — — Transportation services received from Spire NGL Inc. 1.0 1.0 1.0 In the twelve months ended September 30, 2020, Spire Alabama had natural gas purchases from and sales to Spire Marketing totaling $6.3 and $0.3, respectively. ACCOUNTS RECEIVABLE AND ALLOWANCE FOR DOUBTFUL ACCOUNTS – Trade accounts receivable are recorded at the amounts due from customers, including unbilled amounts. Estimates of the collectability of trade accounts receivable are based on historical trends, age of receivables, economic conditions, credit risk of specific customers, and other factors. Accounts receivable are written off against the allowance for doubtful accounts when they are deemed to be uncollectible. Spire Spire Missouri Spire Alabama 2020 2019 2018 2020 2019 2018 2020 2019 2018 Allowance at beginning of year $ 23.0 $ 22.4 $ 18.3 $ 14.9 $ 16.0 $ 14.1 $ 6.3 $ 3.9 $ 2.6 Additions charged to expense 14.0 16.9 14.6 12.7 12.3 11.9 0.9 4.7 2.1 Net deductions (12.1 ) (16.3 ) (10.5 ) (9.5 ) (13.4 ) (10.0 ) (1.7 ) (2.3 ) (0.8 ) Allowance at end of year $ 24.9 $ 23.0 $ 22.4 $ 18.1 $ 14.9 $ 16.0 $ 5.5 $ 6.3 $ 3.9 FINANCE RECEIVABLES – Spire Alabama finances third party contractor sales of merchandise including gas furnaces and appliances. At September 30, 2020 and September 30, 2019, Spire Alabama’s finance receivable totaled approximately $9.4 and $11.7, respectively. Financing is available only to qualified customers who meet creditworthiness thresholds for customer payment history and external agency credit reports. Spire Alabama relies upon ongoing payments as the primary indicator of credit quality during the term of each contract. The allowance for credit losses is recognized using an estimate of write-off percentages based on historical experience. Delinquent accounts are evaluated on a case-by-case basis and, absent evidence of debt repayment, after 90 days are due in full and assigned to a third-party collection agency. The remaining finance receivable is written off approximately 12 months after being assigned to the third-party collection agency. Spire Alabama had finance receivables past due 90 days or more of $0.3 at September 30, 2020 and $0.4 at September 30, 2019. GROUP MEDICAL AND WORKERS’ COMPENSATION RESERVES – The Company self-insures its group medical and workers’ compensation costs and carries stop-loss coverage in relation to medical claims and workers’ compensation claims. Reserves for amounts incurred but not reported are established based on historical cost levels and lags between occurrences and reporting. FAIR VALUE MEASUREMENTS – Certain assets and liabilities are recognized or disclosed at fair value, which is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). GAAP establishes a fair value hierarchy that prioritizes the inputs used to measure fair value. The levels of the hierarchy are described below: • Level 1 – Unadjusted quoted prices in active markets for identical assets or liabilities. • Level 2 – Pricing inputs other than quoted prices included within Level 1, which are either directly or indirectly observable for the asset or liability as of the reporting date. These inputs are derived principally from, or corroborated by, observable market data. • Level 3 – Pricing that is based upon inputs that are generally unobservable that are based on the best information available and reflect management’s assumptions about how market participants would price the asset or liability. Assessment of the significance of a particular input to the fair value measurements may require judgment and may affect the valuation of the asset or liability and its placement within the fair value hierarchy. Additional information about fair value measurements is provided in Note 8 , Fair Value of Financial Instruments, Note 9 , Fair Value Measurements, and Note 13 , Pension Plans and Other Postretirement Benefits. STOCK-BASED COMPENSATION – The Company accounts for share-based compensation arrangements in accordance with ASC Topic 718, Compensation - Stock Compensation . The Company measures stock-based compensation awards at fair value at the date of grant and recognizes the compensation cost of the awards over the requisite service period. Forfeitures are recognized in the period they occur. Refer to Note 3 , Stock-Based Compensation, for further discussion of the accounting for the Company’s stock-based compensation plans. NEW ACCOUNTING PRONOUNCEMENTS – Spire, Spire Missouri and Spire Alabama adopted the guidance in ASU No. 2014-09, Revenue from Contracts with Customers , and related amendments (collectively, “ASC 606”), in the first quarter of fiscal year 2019 using the modified retrospective method applied to all contracts at October 1, 2018. The core principle of ASC 606 is that revenue should be recognized to depict the transfer of control of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Under the new standard, an entity must identify the performance obligations in a contract, determine the transaction price and allocate the price to specific performance obligations to recognize revenue when the obligation is completed. In addition, ASC 606 requires disclosure of the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. The adoption of ASC 606 resulted in no change to how Spire, Spire Missouri and Spire Alabama recognize revenue, and therefore, no cumulative effect adjustment to the opening balance of retained earnings was required, and there was no significant impact to financial results after adoption. The adoption did result in changes to the disclosures about revenue, which are included in Note 2 , Revenue. Some revenue arrangements, such as alternative revenue programs and certain derivative contracts, are excluded from the scope of ASC 606 and, therefore, are presented separately in disclosures. Also effective October 1, 2018, Spire, Spire Missouri and Spire Alabama adopted ASU No. Compensation – Retirement Benefits : Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost The amended guidance that the of net periodic pension and postretirement benefit costs presented within line item in the income statement as other compensation costs (except for the amount being capitalized), while other components presented outside the subtotal of operating income and . The amended guidance is applied retrospectively for income statement presentation and prospectively for capitalization. The Company, Spire practical expedient permitting the use of the amounts disclosed in its pension and other postretirement benefit plan note for the prior comparative periods as the estimation basis for applying the retrospective presentation requirements. Accordingly, for the year ended September 30, 2018, the Company, Spire Missouri and Spire Alabama reclassified net benefit costs (income) of $14.4, $17.2 and $(2.0), respectively, from “operation and maintenance” to “other income (expense), net.” For Spire Missouri, Spire Alabama, and the Company’s other rate-regulated entities, all components of net benefit cost have historically been recovered from customers as a component of utility plant and will continue to be recovered in the same manner over the depreciable lives of the related plant assets; therefore, for those entities, the components that are no longer eligible to be capitalized as a component of plant under GAAP are reported as regulatory assets In February 201 8 , the FASB issued ASU 201 8 -02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income . This guidance permits companies to make an election to reclassify stranded income tax effects from the enact ment of the Tax Cuts and Jobs Act of 2017, included in accumulated other comprehensive income or loss (AOCI) , to retained earnings. The Company, Spire Missouri and Spire Alabama adopt ed this guidance in the quarter ended September 30, 201 8 , and the related reclassifications are shown on the statements of shareholders’ equity of the Company and Spire Missouri. There was no effect for Spire Alabama. The Company, Spire Missouri and Spire Alabama adopted ASU No. 2016-02, Leases Note 17 , Leases. Spire, Spire Missouri and Spire Alabama adopted the guidance in ASU No. 2017-12, Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses: Measurement of Credit Losses on Financial Instruments RECLASSIFICATIONS – Spire’s consolidated statements of income historically showed Gas Utility operating revenues and expense line items separately from Gas Marketing and other operations. The current presentation shows operating revenues and expense line items on a consolidated basis. Disaggregated data is presented in Note 14 , Information by Operating Segment. Prior period amounts have been reclassified to conform with the current period presentation.

Revenue

Revenue	12 Months Ended
	Sep. 30, 2020
Revenue From Contract With Customer [Abstract]
Revenue	2. REVENUE The following tables show revenue disaggregated by source and customer type. 2020 2019 Spire Gas Utility: Residential $ 1,184.3 $ 1,267.3 Commercial & industrial 383.0 433.9 Transportation 115.8 112.1 Off-system & other incentive 38.4 41.9 Other customer revenue 26.2 22.5 Total revenue from contracts with customers 1,747.7 1,877.7 Changes in accrued revenue under alternative revenue programs 4.3 (16.9 ) Total Gas Utility operating revenues 1,752.0 1,860.8 Gas Marketing: Revenue from contracts with retail customers 87.9 83.7 Revenue from wholesale derivative contracts — — Total Gas Marketing operating revenues 87.9 83.7 Other 57.8 21.5 Total before eliminations 1,897.7 1,966.0 Intersegment eliminations (see Note 14, Information by Operating Segment) (42.3 ) (13.6 ) Total Operating Revenues $ 1,855.4 $ 1,952.4 Spire Missouri Residential $ 859.6 $ 945.9 Commercial & industrial 241.4 283.8 Transportation 32.9 33.1 Off-system & other incentive 35.1 41.9 Other customer revenue 22.3 — Total revenue from contracts with customers 1,191.3 1,304.7 Changes in accrued revenue under alternative revenue programs 2.3 (12.9 ) Total Operating Revenues $ 1,193.6 $ 1,291.8 Spire Alabama Residential $ 267.8 $ 265.3 Commercial & industrial 109.4 113.5 Transportation 72.9 69.5 Off-system & other incentive 3.2 — Other customer revenue 1.9 20.7 Total revenue from contracts with customers 455.2 469.0 Changes in accrued revenue under alternative revenue programs (0.2 ) (3.5 ) Total Operating Revenues $ 455.0 $ 465.5 The Utilities sell natural gas to residential and other customers. The sale of natural gas is governed by the various state utility commissions, which set rates, charges, and terms and conditions of service, collectively included in a “tariff.” The performance obligation, which relates to the promise to provide natural gas, is satisfied over time as the customer simultaneously receives and consumes the natural gas, and revenue is recognized accordingly. The Utilities’ transportation revenue relates to the promise to transport the specified quantities of natural gas at tariff rates. This performance obligation is satisfied over time as the gas is transported, and revenue is recognized as invoiced monthly. The Utilities have alternative revenue programs (ARPs), which represent an agreement between the utility and its regulator, currently consisting of decoupling mechanisms (also known as weather normalization adjustments) and incentive programs (primarily Alabama’s Cost Control Measure). When the criteria to recognize additional (or reduced) revenue from ARPs have been met, the Utilities establish a regulatory asset (or liability). When amounts previously recognized for ARPs are billed, the Utilities reduce the regulatory asset (or liability) and increase (or decrease) accounts receivable. Billed amounts, which are part of the overall tariff paid by customers, are included in revenue from contracts with customers, while the change in the related regulatory asset or liability is presented as revenue from ARPs. Depending on whether the beginning accrued ARP balance was a regulatory asset or liability and depending on the size and direction of the current period accrual, the amount presented as revenue from ARPs could be negative. The Utilities read meters and bill customers on monthly cycles. Spire Missouri, Spire Gulf and Spire Mississippi record their gas utility revenues from gas sales and transportation services on an accrual basis that includes estimated amounts for gas delivered but not yet billed. The accruals for unbilled revenues are reversed in the subsequent accounting period when meters are actually read and customers are billed. Spire Alabama records natural gas distribution revenues in accordance with the tariff established by the APSC. Unbilled revenue is accrued in an amount equal to the related gas cost, as profit margin is not considered earned until billed. Spire’s other subsidiaries, including Spire Marketing, record revenues when earned, as the product is delivered or as services are performed. Gas Marketing’s contracts are derivatives. The wholesale contracts (with producers, municipalities, and utility companies) are subject to derivative accounting. The retail contracts (with large commercial and industrial customers) are designated as “normal purchase, normal sale” arrangements and are therefore accounted for as revenue from contracts with customers. The performance obligation is satisfied over time by the transfer of control of natural gas to the customer, and revenue is recognized as invoiced monthly. Payments are generally required within 30 days of billing, and contracts generally do not have a significant financing component. Spire’s revenues are not subject to significant returns, refunds, or warranty obligations. Spire, Spire Missouri, and Spire Alabama have elected to apply a “right to invoice” practical expedient, recognizing revenue for volumes delivered for which they have a right to invoice, as long as that amount corresponds with the value to the customer. Disclosures about remaining performance obligations are not required because either contracts have an original expected duration of one year or less, or revenue is recognized under the right to invoice practical expedient, or both. Sales taxes imposed on applicable Spire Alabama and Spire Missouri sales are billed to customers. These amounts are not recorded in the statements of income but are recorded as tax collections payable and included in the “Other” line of the Current Liabilities section of the balance sheets. Gross receipts taxes associated with the Company’s natural gas utility services are imposed on the Company, Spire Missouri, and Spire Alabama and billed to its customers. The expense amounts (shown in the table below) are reported gross in the “Taxes, other than income taxes” line in the statements of income, and corresponding revenues are reported in “Operating Revenues.” 2020 2019 2018 Spire $ 91.5 $ 99.3 $ 98.4 Spire Missouri 63.5 71.1 68.9 Spire Alabama 23.3 23.7 25.4

Stock-based Compensation

Stock-based Compensation	12 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	3. STOCK-BASED COMPENSATION The Spire 2015 Equity Incentive Plan (EIP) was approved by shareholders of Spire on January 29, 2015 and amended on November 9, 2018. The purpose of the EIP is to encourage directors, officers, and key employees of the Company and its subsidiaries to contribute to the Company’s success and align their interests with that of shareholders. To accomplish this purpose, the Compensation Committee (“Committee”) of Spire’s Board of Directors (the “Board”) may grant awards under the EIP that may be earned by achieving performance objectives and/or other criteria as determined by the Committee. Under the terms of the EIP, officers and employees of the Company and its subsidiaries, as determined by the Committee, are eligible to be selected for awards. The EIP provides for restricted stock, restricted stock units, qualified and non-qualified stock options, stock appreciation rights, and performance shares payable in stock, cash, or a combination of both. The EIP generally provides a minimum vesting period of at least three years for each type of award, with pro rata vesting permitted during the minimum three-year vesting period. The maximum number of shares reserved for issuance under the EIP is 1,000,000. The Company issues new shares to satisfy employee restricted stock awards. Restricted Stock Awards During fiscal 2020, the Company granted 91,662 performance-contingent restricted share units to executive officers and key employees at a weighted average grant date fair value of $76.19 per share. This number represents the target shares that can be earned pursuant to the terms of the awards. The share units have a performance period ending September 30, 2023. While the participants have no interim voting rights on these share units, dividends accrue during the performance period and are paid to the participants upon vesting but are subject to forfeiture if the underlying share units do not vest. The number of share units that will ultimately vest is dependent upon the attainment of certain levels of earnings and other strategic goals, as well as the Company’s level of total shareholder return (TSR) during the performance period relative to a comparator group of peer companies. This TSR provision is considered a market condition under GAAP and is discussed further below. The maximum amount of shares that can be earned pursuant to the terms of the awards is 200% of the target units granted. The weighted average grant date fair value of performance-contingent restricted share units granted during fiscal years 2019 and 2018 was $80.72 and $79.88 per share, respectively. Fiscal 2020 activity of restricted stock units subject to performance and/or market conditions is presented below: Units Weighted Average Grant Date Fair Value Per Unit Nonvested at September 30, 2019 263,910 $ 73.20 Granted 91,662 $ 76.19 Vested (86,287 ) $ 58.68 Forfeited (9,341 ) $ 79.34 Nonvested at September 30, 2020 259,944 $ 78.92 For the year ended September 30, 2020, the total number of shares that could be issued if all outstanding award grants attain maximum performance payout is 519,888. During fiscal 20 20 , the Company granted 33,350 shares of time-vested restricted stock to executive officers and key employees at a weighted average grant date fair value of $ 76.13 per share. Unless forfeited based on terms of the agreements, these shares will vest in fiscal 2021. In the interim, participants receive full voting rights and dividends, which are not subject to forfeiture. The weighted average grant date fair value of time-vested restricted stock and restricted stock units awarded to employees during fiscal years 201 9 and 201 8 was $ and $ 76.60 per share, respectively. During fiscal 2020, the Company granted 10,560 shares of time-vested restricted stock to non-employee directors at a weighted average grant date fair value of $84.58 per share. These shares vested in fiscal 2020, six months after the grant date. The weighted average grant date fair value of restricted stock awarded to non-employee directors during fiscal years 2019 and 2018 was $78.69 and $63.20 per share, respectively. Time-vested restricted stock and stock unit activity for fiscal 2020 is presented below: Shares/ Units Weighted Average Grant Date Fair Value Per Share Nonvested at September 30, 2019 96,277 $ 72.83 Granted 33,350 $ 76.13 Vested (32,326 ) $ 65.28 Forfeited (3,628 ) $ 76.94 Nonvested at September 30, 2020 93,673 $ 76.45 For restricted stock and stock units (performance-contingent and time-vested) that vested during fiscal years 2020, 2019, and 2018, the Company withheld 41,353 shares, 28,731 shares and 34,922 shares, respectively, at weighted average prices of $77.07, $79.23 and $81.65 per share, respectively, pursuant to elections by employees to satisfy tax withholding obligations. The total fair value of restricted stock (performance-contingent and time-vested) that vested during fiscal years 2020, 2019, and 2018 was $9.8, $7.6, and $10.5, respectively, and the related tax benefit was $3.7, $2.9, and $4.0, respectively. None of the tax benefits have been realized. In fiscal 2019, the Company gave participants in the EIP the ability to defer a portion or all of their award. Participants have elected to defer 59,408 shares and 80,760 shares (at target payout) in fiscal years 2020 and 2019, respectively. Based on actual performance, these awards will be issued in cash, not shares, once the performance requirements have been achieved, so related amounts are reflected as temporary equity on the consolidated balance sheet. Equity Compensation Costs Compensation cost for performance-contingent restricted stock and stock unit awards is based upon the probable outcome of the performance conditions. For shares or units that do not vest or that are not expected to vest due to the outcome of the performance conditions (excluding market conditions), no compensation cost is recognized and any previously recognized compensation cost is reversed. The fair value of awards of performance-contingent and time-vested restricted stock and restricted stock units, not subject to the TSR provision, are estimated using the closing price of the Company’s stock on the grant date. For those awards that do not pay dividends during the vesting period, the estimate of fair value is reduced by the present value of the dividends expected to be paid on the Company’s common stock during the performance period, discounted using an appropriate U.S. Treasury yield. For shares subject to the TSR provision, the estimated impact of this market condition is reflected in the grant date fair value per share of the awards. Accordingly, compensation cost is not reversed to reflect any actual reductions in the awards that may result from the TSR provision. However, if the Company’s TSR during the performance period ranks below the level specified in the award agreements, relative to a comparator group of companies, and the Committee elects not to reduce the award (or reduce by a lesser amount), this election would be accounted for as a modification of the original award and additional compensation cost would be recognized at that time. The grant date fair value of the awards subject to the TSR provision awarded during fiscal years 2020, 2019 and 2018 was valued by a Monte Carlo simulation model that assessed the probabilities of various TSR outcomes. The significant assumptions used in the Monte Carlo simulations are as follows: 2020 2019 2018 Risk-free interest rate 1.57% 2.88% 1.76% Expected dividend yield of stock — — — Expected volatility of stock 16.8% 17.0% 16.0% Vesting period 3.0 years 3.0 years 2.9 years The risk-free interest rate was based on the yield on U.S. Treasury securities matching the vesting period. A zero percent dividend yield was used, which is mathematically equivalent to the assumption that dividends are reinvested as they are paid. The expected volatility is based on the historical volatility of the Company’s stock. Volatility assumptions were also made for each of the companies included in the comparator group. The vesting period is equal to the performance period set forth in the terms of the award. The amounts of compensation cost recognized for share-based compensation arrangements are presented below: 2020 2019 2018 Total compensation cost $ 9.4 $ 8.6 $ 6.9 Compensation cost capitalized (0.6 ) (1.4 ) (1.3 ) Prior period disallowed stock compensation capitalization — — 6.9 Compensation cost recognized in net income 8.8 7.2 12.5 Income tax benefit recognized in net income (2.1 ) (1.7 ) (4.0 ) Compensation cost recognized in net income, net of income tax $ 6.7 $ 5.5 $ 8.5 As of September 30, 2020, there was $10.8 of total unrecognized compensation cost related to non-vested share-based compensation arrangements, which is expected to be recognized over a weighted average period of 1.75 years.

Earnings Per Common Share

Earnings Per Common Share	12 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Earnings Per Common Share	4. EARNINGS PER COMMON SHARE 2020 2019 2018 Basic Earnings Per Common Share: Net Income $ 88.6 $ 184.6 $ 214.2 Less: Provision for preferred dividends 14.8 5.3 — Income allocated to participating securities 0.1 0.4 0.5 Net Income Available to Common Shareholders $ 73.7 $ 178.9 $ 213.7 Weighted Average Common Shares Outstanding (in millions) 51.2 50.7 49.1 Basic Earnings Per Share of Common Stock $ 1.44 $ 3.53 $ 4.35 Diluted Earnings per Common Share: Net Income $ 88.6 $ 184.6 $ 214.2 Less: Provision for preferred dividends 14.8 5.3 — Income allocated to participating securities 0.1 0.4 0.5 Net Income Available to Common Shareholders $ 73.7 $ 178.9 $ 213.7 Weighted Average Common Shares Outstanding (in millions) 51.2 50.7 49.1 Dilutive Effect of Restricted Stock and Restricted Stock Units (in millions)* 0.1 0.1 0.2 Weighted Average Diluted Common Shares (in millions) 51.3 50.8 49.3 Diluted Earnings Per Share of Common Stock $ 1.44 $ 3.52 $ 4.33 * Calculation excludes certain outstanding common shares (shown in millions by period at the right) attributable to stock units subject to performance or market conditions and restricted stock, which could have a dilutive effect in the future 0.1 0.1 0.4

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Sep. 30, 2020
Stockholders Equity Note [Abstract]
Shareholders' Equity	5. SHAREHOLDERS’ EQUITY Spire Preferred Stock At September 30, 2020 and 2019, Spire had authorized 5,000,000 shares of preferred stock. On May 21, 2019, Spire completed the public offering of 10,000,000 depositary shares (the “Depositary Shares”), each representing a 1/1,000th Dividends on the Preferred Stock, when declared by the Board, will be payable on the liquidation preference amount, on a cumulative basis, quarterly in arrears on the 15th day of February, May, August and November of each year, beginning on August 15, 2019. Dividends will be payable out of amounts legally available for the payment of dividends at an annual rate equal to 5.90% of the liquidation preference per share of Preferred Stock (equivalent to $25.00 per Depositary Share). Dividends will accumulate daily and be cumulative from May 21, 2019. Under the terms of the Preferred Stock, the Company’s ability to declare or pay dividends on, or purchase or redeem, shares of its common stock or any class or series of capital stock of the Company that rank junior to the Preferred Stock will be subject to certain restrictions in the event that the Company does not declare and pay the full cumulative dividends on the Preferred Stock through the most recently completed quarterly dividend period. Spire may, at its option, redeem the Preferred Stock (i) in whole, but not in part, at any time prior to August 15, 2024, within 120 days after a ratings event where a rating agency amends, clarifies or changes the criteria it uses to assign equity credit for securities such as the Preferred Stock, at a redemption price in cash equal to $25,500 per share, or (ii) in whole or in part, from time to time, on or after August 15, 2024, at a redemption price in cash equal to $25,000 per share, plus, in each case, all accumulated and unpaid dividends (whether declared or not) up to such redemption date. Shareholders of the Preferred Stock generally have no voting rights with respect to matters that generally require the approval of voting stockholders. The limited voting rights of holders of the Preferred Stock include the right to vote on certain matters that may affect the preference or special rights of the Preferred Stock. In addition, if and whenever dividends on any shares of Preferred Stock have not been declared and paid for at least six dividend periods, whether or not consecutive, the number of directors then constituting the Board shall automatically be increased by two (to be elected by the holders of the Preferred Stock) until all accumulated and unpaid dividends on the Preferred Stock have been paid in full. ATM Program On February 6, 2019, Spire entered into an at-the-market (ATM) equity distribution agreement, supplemented as of May 14, 2019, pursuant to which the Company may offer and sell, from time to time, shares of its common stock having an aggregate offering price of up to $150.0. Proceeds from this program are intended to be used (i) to fund, in part, investments related to the construction of infrastructure and infrastructure improvements in the Utilities, as well as pipelines and storage, and (ii) for general corporate purposes, including repayment of short-term debt and the adjustment from time to time of the Company’s capital structure. Under this program, for the year ended September 30, 2020, Spire issued 446,619 shares, generating $32.0 of proceeds net of issuance costs, and for the year ended September 30, 2019 , Other Equity Information Spire has a shelf registration statement on Form S-3 on file with the U.S. Securities and Exchange Commission (SEC) for the issuance and sale of up to 250,000 shares of common stock under its Dividend Reinvestment and Direct Stock Purchase Plan. There were 207,254 and 201,148 shares at September 30, 2020 and November 13, 2020, respectively, remaining available for issuance under this Form S-3. Spire also has a universal shelf registration statement on Form S-3 on file with the SEC for the issuance of various equity and debt securities, which expires on May 14, 2022. Spire Missouri Substantially all of Spire Missouri’s plant is subject to the liens of its first mortgage bonds. The mortgage contains several restrictions on Spire Missouri’s ability to pay cash dividends on its common stock or to make loans to its parent company. These mortgage restrictions are applicable regardless of whether the stock is publicly held or held solely by Spire Missouri’s parent company. Under the most restrictive of these provisions, no cash dividend may be declared or paid if, after the dividend, the aggregate net amount spent for all dividends after September 30, 1953 would exceed a maximum amount determined by a formula set out in the mortgage. Under that formula, the maximum amount is the sum of $8.0 plus earnings applicable to common stock (adjusted for stock repurchases and issuances) for the period from September 30, 1953 to the last day of the quarter before the declaration or payment date for the dividends. As of September 30, 2020 and 2019, the amount under the mortgage’s formula that was available to pay dividends was $1,269.4 and $1,182.4, respectively. Thus, all of Spire Missouri’s retained earnings were free from such dividend restrictions as of those dates. Spire Missouri has a universal shelf registration statement on Form S-3 on file with the SEC for the issuance of various equity and debt securities, which expires on May 14, 2022. Spire Missouri was authorized by the MoPSC to issue registered securities (first mortgage bonds, unsecured debt and preferred stock), common stock, and private placement debt in an aggregate amount of up to $500.0 for financings placed any time before September 30, 2021. As of September 30, 2020, $125.0 At September 30, 2020 and 2019, Spire Missouri had authorized 1,480,000 shares of preferred stock, but none were issued and outstanding. Spire Alabama At September 30, 2020 and 2019, Spire Alabama had authorized 120,000 shares of preferred stock, but none were issued and outstanding. Accumulated Other Comprehensive Income The components of accumulated other comprehensive income (AOCI), net of income taxes, recognized in the balance sheets at September 30 were as follows: Net Unrealized Gains (Losses) on Cash Flow Hedges Defined Benefit Pension and Other Postretirement Benefit Plans Net Unrealized Losses on Available-for- Sale Debt Securities Total Spire Balance at September 30, 2018 $ 7.9 $ (1.5 ) $ — $ 6.4 Other comprehensive (loss) income (36.9 ) (0.9 ) 0.1 (37.7 ) Balance at September 30, 2019 (29.0 ) (2.4 ) 0.1 (31.3 ) Other comprehensive loss (9.4 ) (0.5 ) — (9.9 ) Balance at September 30, 2020 $ (38.4 ) $ (2.9 ) $ 0.1 $ (41.2 ) Spire Missouri Balance at September 30, 2018 $ — $ (1.6 ) $ — $ (1.6 ) Other comprehensive loss — (0.8 ) — (0.8 ) Balance at September 30, 2019 — (2.4 ) — (2.4 ) Other comprehensive loss — (0.5 ) — (0.5 ) Balance at September 30, 2020 $ — $ (2.9 ) $ — $ (2.9 ) Income tax expense (benefit) recorded for items of other comprehensive income (loss) reported in the statements of comprehensive income is calculated by applying statutory federal, state, and local income tax rates applicable to ordinary income. The tax rates applied to individual items of other comprehensive income (loss) are similar within each reporting period. For the periods presented, Spire Alabama had no AOCI balances.

Long-term Debt

Long-term Debt	12 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Long-term Debt	6. LONG-TERM DEBT The composition of long-term debt as of September 30 is shown in the following tables. 2020 2019 Spire 2.52% Senior Notes, due September 1, 2021 $ 35.0 $ 35.0 3.31% Notes Payable, due December 15, 2022 25.0 25.0 3.54% Senior Notes, due February 27, 2024 150.0 150.0 3.13% Senior Notes, due September 1, 2026 130.0 130.0 3.93% Senior Notes, due March 15, 2027 100.0 100.0 4.70% Senior Notes, due August 15, 2044 250.0 250.0 Total principal of Spire Missouri long-term debt (see below) 1,098.0 930.0 Total principal of Spire Alabama long-term debt (see below) 475.0 415.0 Other subsidiaries' long-term debt: 4.14% First Mortgage Bonds, due September 30, 2021 20.0 20.0 5.00% First Mortgage Bonds, due September 30, 2031 42.0 42.0 2.95% Notes, with annual principal payments through December 2034 135.0 — 3.52% First Mortgage Bonds, due September 30, 2049 40.0 40.0 Total principal of long-term debt 2,500.0 2,137.0 Less: Unamortized discounts and debt issuance costs (15.9 ) (14.4 ) Less: Current portion (60.4 ) (40.0 ) Long-term debt, excluding current portion $ 2,423.7 $ 2,082.6 Spire Missouri Floating-rate note due December 1, 2021 $ — $ 100.0 First Mortgage Bonds: 3.00% Series, due March 15, 2023 55.0 55.0 3.40% Series, due August 15, 2023 250.0 250.0 3.40% Series, due March 15, 2028 45.0 45.0 7.00% Series, due June 1, 2029 19.3 25.0 2.84% Series, due November 15, 2029 275.0 — 7.90% Series, due September 15, 2030 30.0 30.0 3.68% Series, due September 15, 2032 50.0 50.0 6.00% Series, due May 1, 2034 99.3 100.0 6.15% Series, due June 1, 2036 54.5 55.0 4.63% Series, due August 15, 2043 99.9 100.0 4.23% Series, due September 15, 2047 70.0 70.0 4.38% Series, due September 15, 2057 50.0 50.0 Total principal of Spire Missouri long-term debt 1,098.0 930.0 Less: Unamortized discounts and debt issuance costs (6.0 ) (5.0 ) Less: Current portion — — Spire Missouri long-term debt, excluding current portion $ 1,092.0 $ 925.0 Spire Alabama 5.20% Notes, due January 15, 2020 $ — $ 40.0 3.86% Notes, due December 22, 2021 50.0 50.0 3.21% Notes, due September 15, 2025 35.0 35.0 2.88% Notes, due December 1, 2029 100.0 — 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 475.0 415.0 Less: Unamortized discounts and debt issuance costs (3.2 ) (2.8 ) Less: Current portion — (40.0 ) Spire Alabama long-term debt, excluding current portion $ 471.8 $ 372.2 Maturities of long-term debt for Spire on a consolidated basis, Spire Missouri and Spire Alabama for the five fiscal years after September 30, 2020 are as follows: 2021 2022 2023 2024 2025 Spire $ 60.4 $ 55.8 $ 336.2 $ 156.6 $ 42.0 Spire Missouri — — 305.0 — — Spire Alabama — 50.0 — — 35.0 The long-term debt agreements of Spire, Spire Missouri and Spire Alabama contain customary financial covenants and default provisions. As of September 30, 2020, there were no events of default under these financial covenants. Spire At September 30, 2020, including the current portion but excluding unamortized discounts and debt issuance costs, Spire had long-term debt totaling $2,500.0, of which $1,098.0 was issued by Spire Missouri, $475.0 was issued by Spire Alabama and $237.0 was issued by other subsidiaries. All long-term debt bears fixed rates and is subject to changes in fair value as market interest rates change. However, increases and decreases in fair value would impact earnings and cash flows only if the Company were to reacquire any of these issues in the open market prior to maturity. Under GAAP applicable to the Utilities’ regulated operations, losses or gains on early redemption of long-term debt would typically be deferred as regulatory assets or regulatory liabilities and amortized over a future period. Interest expense shown on Spire’s consolidated statement of income is net of capitalized interest totaling $5.8, $6.8 and $2.6 for the years ended September 30, 2020, 2019 and 2018, respectively. As indicated in Note 5 Spire Missouri At September 30, 2020, including the current portion (none) but excluding unamortized discounts and debt issuance costs, Spire Missouri had long-term debt totaling $1,098.0. All long-term debt bears fixed rates and is subject to changes in fair value as market interest rates change. Interest expense shown on Spire Missouri’s statement of comprehensive income is net of capitalized interest totaling $0.8, $1.9 and $0.9 for the years ended September 30, 2020, 2019 and 2018, respectively. As indicated in Note 5 Substantially all of Spire Missouri’s plant is subject to the liens of its first mortgage bonds. The mortgage contains several restrictions on Spire Missouri’s ability to pay cash dividends on its common stock, which are described in Note 5 Spire Alabama At September 30, 2020, including the current portion but excluding unamortized debt issuance costs, Spire Alabama had fixed-rate long-term debt totaling $475.0. While these long-term debt issues are fixed-rate, they are subject to changes in fair value as market interest rates change. Interest expense shown on Spire Alabama’s statement of income is net of capitalized interest totaling $1.9 for the year ended September 30, 2020. Because Spire Alabama has no standing authority to issue long-term debt, it must petition the APSC for each planned issuance. On March 24, 2020, the APSC approved an application for up to $150.0 of additional long-term debt financing.

Notes Payable and Credit Agreem

Notes Payable and Credit Agreements	12 Months Ended
	Sep. 30, 2020
Short Term Borrowings [Abstract]
Notes Payable and Credit Agreements	7. NOTES PAYABLE AND CREDIT AGREEMENTS Spire, Spire Missouri and Spire Alabama have a syndicated revolving credit facility pursuant to a loan agreement with 11 banks, expiring October 31, 2023. The loan agreement has an aggregate credit commitment of $975.0, including sublimits of $300.0 for Spire, $475.0 for Spire Missouri and $200.0 for Spire Alabama. These sublimits may be reallocated from time to time among the three borrowers within the $975.0 aggregate commitment, with commitment fees applied for each borrower relative to its credit rating. Spire may use its line to provide for the funding needs of various subsidiaries. The agreement also contains financial covenants limiting each borrower’s consolidated total debt, including short-term debt, to no more than 70% of its total capitalization. As defined in the line of credit, on September 30, 2020, total debt was less than 60% of total capitalization for each borrower. Spire has a commercial paper program (“CP Program”) pursuant to which it may issue short-term, unsecured commercial paper notes. Amounts available under the CP Program may be borrowed, repaid and re-borrowed from time to time, with the aggregate face or principal amount of the notes outstanding under the CP Program at any time not to exceed $975.0. The notes may have maturities of up to 365 days from date of issue. On March 26, 2020, Spire entered into a new loan agreement with two banks providing for a term loan of $150.0, which was immediately fully funded and matures on March 25, 2021, subject to optional prepayment by Spire. The term loan bears interest at the LIBOR Rate (as defined in the loan agreement) plus 0.85% per annum. Proceeds were used for working capital and general corporate purposes. Information about Spire’s consolidated short-term borrowings and about Spire Missouri’s and Spire Alabama’s borrowings from Spire is presented in the following table. As of September 30, 2020, $449.8 of Spire’s short-term borrowings were used to support lending to the Utilities. Spire (Parent Only) Spire Missouri Spire Alabama Spire Credit Term CP Credit Spire Credit Spire Consol- Facility Loan Program Facility Note Facility Note idated Year Ended September 30, 2020 Weighted average borrowings $ 0.1 $ 77.5 $ 476.1 $ 17.9 $ 242.0 $ 4.6 $ 89.0 $ 576.2 Lowest borrowings outstanding — — 73.5 — 16.0 — 18.5 432.6 Highest borrowings outstanding 23.1 150.0 856.6 185.1 429.5 50.0 161.3 856.6 Weighted average interest rate 1.9 % 1.6 % 1.7 % 1.9 % 1.5 % 1.9 % 1.4 % 1.7 % As of September 30, 2020 Borrowings outstanding $ — $ 150.0 $ 498.0 $ — $ 301.2 $ — $ 121.3 $ 648.0 Weighted average interest rate n/a 1.1 % 0.2 % n/a 0.2 % n/a 0.2 % 0.6 % As of September 30, 2019 Borrowings outstanding $ — $ — $ 743.2 $ — $ 386.4 $ — $ 128.7 $ 743.2 Weighted average interest rate n/a n/a 2.3 % n/a 2.3 % n/a 2.3 % 2.3 %

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	8. FAIR VALUE OF FINANCIAL INSTRUMENTS The carrying amounts and estimated fair values of financial instruments not measured at fair value on a recurring basis were as follows: Classification of Estimated Fair Value Carrying Amount Fair Value Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Spire As of September 30, 2020 Cash and cash equivalents $ 4.1 $ 4.1 $ 4.1 $ — Notes payable 648.0 648.0 — 648.0 Long-term debt, including current portion 2,484.1 2,908.6 — 2,908.6 As of September 30, 2019 Cash and cash equivalents $ 5.8 $ 5.8 $ 5.8 $ — Notes payable 743.2 743.2 — 743.2 Long-term debt, including current portion 2,122.6 2,373.4 — 2,373.4 Spire Missouri As of September 30, 2020 Notes payable - associated companies $ 301.2 $ 301.2 $ — $ 301.2 Long-term debt 1,092.0 1,313.5 — 1,313.5 As of September 30, 2019 Cash and cash equivalents $ 2.6 $ 2.6 $ 2.6 $ — Notes payable - associated companies 386.4 386.4 — 386.4 Long-term debt 925.0 1,065.2 — 1,065.2 Spire Alabama As of September 30, 2020 Notes payable - associated companies $ 121.3 $ 121.3 $ — $ 121.3 Long-term debt, including current portion 471.8 576.9 — 576.9 As of September 30, 2019 Notes payable - associated companies $ 128.7 $ 128.7 $ — $ 128.7 Long-term debt, including current portion 412.2 474.8 — 474.8

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	9. FAIR VALUE MEASUREMENTS The information presented below categorizes the assets and liabilities in the balance sheets that are accounted for at fair value on a recurring basis in periods subsequent to initial recognition. The mutual funds included in Level 1 are valued based on exchange-quoted market prices of individual securities. The mutual funds included in Level 2 are valued based on the closing net asset value per unit. Derivative instruments included in Level 1 are valued using quoted market prices on the NYMEX or the Intercontinental Exchange (ICE). Derivative instruments classified in Level 2 include physical commodity derivatives that are valued using broker or dealer quotation services whose prices are derived principally from, or are corroborated by, observable market inputs. Also included in Level 2 are certain derivative instruments that have values that are similar to, and correlate with, quoted prices for exchange-traded instruments in active markets. Derivative instruments included in Level 3 are valued using generally unobservable inputs that are based upon the best information available and reflect management’s assumptions about how market participants would price the asset or liability. There were no material Level 3 balances as of September 30, 2020 or 2019. The Company’s and the Utilities’ policy is to recognize transfers between the levels of the fair value hierarchy, if any, as of the beginning of the interim reporting period in which circumstances change or events occur to cause the transfer. The mutual funds are included in “Other investments” on the Company’s balance sheets and in “Other Property and Investments” on Spire Missouri’s balance sheets. Derivative assets and liabilities, including receivables and payables associated with cash margin requirements, are presented net on the balance sheets when a legally enforceable netting agreement exist between the Company , Spire Missouri or Spire Alabama and the counterparty to the derivative contract. For additional information on derivative instruments, see Note 10 , Derivative Instruments and Hedging Activities. Spire Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Effects of Netting and Cash Margin Receivables /Payables Total As of September 30, 2020 ASSETS Gas Utility: U.S. stock/bond mutual funds $ 21.9 $ — $ — $ — $ 21.9 Gasoline and heating oil contracts 0.3 — — (0.3 ) — NYMEX/ICE natural gas contracts 6.3 — — (6.3 ) — Gas Marketing: NYMEX/ICE natural gas contracts — 27.7 — (25.4 ) 2.3 Natural gas commodity contracts — 14.5 0.4 — 14.9 Other: U.S. stock/bond mutual funds 18.6 — — — 18.6 Total $ 47.1 $ 42.2 $ 0.4 $ (32.0 ) $ 57.7 LIABILITIES Gas Utility: NYMEX/ICE natural gas contracts $ 0.9 $ — $ — $ (0.9 ) $ — Gas Marketing: NYMEX/ICE natural gas contracts 0.7 21.4 — (22.1 ) — Natural gas commodity contracts — 22.3 — — 22.3 Other: Interest rate swaps — 54.2 — — 54.2 Total $ 1.6 $ 97.9 $ — $ (23.0 ) $ 76.5 As of September 30, 2019 ASSETS Gas Utility: U.S. stock/bond mutual funds $ 20.5 $ — $ — $ — $ 20.5 Gas Marketing: NYMEX/ICE natural gas contracts 0.9 6.5 — (6.9 ) 0.5 Natural gas commodity contracts — 16.8 — (2.5 ) 14.3 Other: U.S. stock/bond mutual funds 15.5 — — — 15.5 Total $ 36.9 $ 23.3 $ — $ (9.4 ) $ 50.8 LIABILITIES Gas Utility: NYMEX/ICE natural gas contracts $ 12.3 $ — $ — $ (12.3 ) $ — Gas Marketing: NYMEX/ICE natural gas contracts 0.4 8.5 — (8.9 ) — Natural gas commodity contracts — 13.8 0.1 (2.5 ) 11.4 Other: Interest rate swaps — 43.4 — — 43.4 Total $ 12.7 $ 65.7 $ 0.1 $ (23.7 ) $ 54.8 Spire Missouri Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Effects of Netting and Cash Margin Receivables /Payables Total As of September 30, 2020 ASSETS U.S. stock/bond mutual funds $ 21.9 $ — $ — $ — $ 21.9 Gasoline and heating oil contracts 0.3 — — (0.3 ) — NYMEX/ICE natural gas contracts 6.3 — — (6.3 ) — Total $ 28.5 $ — $ — $ (6.6 ) $ 21.9 LIABILITIES NYMEX/ICE natural gas contracts $ 0.9 $ — $ — $ (0.9 ) $ — As of September 30, 2019 ASSETS U.S. stock/bond mutual funds $ 20.5 $ — $ — $ — $ 20.5 LIABILITIES NYMEX/ICE natural gas contracts $ 12.3 $ — $ — $ (12.3 ) $ — Spire Alabama Spire Alabama occasionally utilizes a gasoline derivative program to stabilize the cost of fuel used in operations. As of September 30, 2020, and September 30, 2019, there were no gasoline derivatives outstanding.

Derivative Instruments and Hedg

Derivative Instruments and Hedging Activities	12 Months Ended
	Sep. 30, 2020
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities	10. DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES Spire Spire Missouri has a risk management policy to utilize various derivatives, including futures contracts, exchange-traded options and swaps for the explicit purpose of managing price risk associated with purchasing and delivering natural gas on a regular basis to customers in accordance with its tariffs. The objective of this policy is to limit Spire Missouri’s exposure to natural gas price volatility and to manage, hedge and mitigate substantial price risk. Further discussion of this policy can be found in the Spire Missouri section. From time to time Spire Missouri and Spire Alabama purchase NYMEX futures and options contracts to help stabilize operating costs associated with forecasted purchases of gasoline and diesel fuels used to power vehicles and equipment. Further information on these derivatives can be found in the Spire Missouri and Spire Alabama sections, respectively. In the course of its business, Spire’s gas marketing subsidiary, Spire Marketing (including a wholly owned subsidiary), enters into commitments associated with the purchase or sale of natural gas. Certain of Spire Marketing’s derivative natural gas contracts are designated as normal purchases or normal sales and, as such, are excluded from the scope of ASC Topic 815 and are accounted for as executory contracts on an accrual basis. Any of Spire Marketing’s derivative natural gas contracts that are not designated as normal purchases or normal sales are accounted for at fair value. At September 30, 2020, the fair values of 278.3 million MMBtu of non-exchange-traded natural gas commodity contracts were reflected in the Consolidated Balance Sheet. Of these contracts, 233.1 million MMBtu will settle during fiscal 2021, and 35.7 million MMBtu, 5.8 million MMBtu, 1.3 million MMBtu, 1.6 million MMBtu, and 0.8 million MMBtu will settle during fiscal years 2022, 2023, 2024, 2025, and 2026, respectively. These contracts have not been designated as hedges; therefore, changes in the fair value of these contracts are reported in earnings each period. Furthermore, Spire Marketing manages the price risk associated with its fixed-priced commitments by either closely matching the offsetting physical purchase or sale of natural gas at fixed prices or through the use of NYMEX or ICE futures, swap, and option contracts to lock in margins. At September 30, 2020, Spire Marketing’s unmatched fixed-price positions were not material to Spire’s financial position or results of operations. Spire Marketing’s NYMEX and ICE natural gas futures, swap and option contracts used to lock in margins may be designated as cash flow hedges of forecasted transactions for financial reporting purposes. In August 2018, Spire entered into a three- year three-year ten-year The Company’s and Spire Missouri’s exchange-traded/cleared derivative instruments consist primarily of NYMEX and ICE positions. The NYMEX is the primary national commodities exchange on which natural gas derivatives are traded. Open NYMEX and ICE natural gas futures and swap positions at September 30, 2020 and 2019 were as follows: September 30, 2020 September 30, 2019 Gas Marketing Notional (MMBtu millions) Maximum Term (Months) Notional (MMBtu millions) Maximum Term (Months) Natural gas futures purchased 22.9 41 29.1 36 Natural gas options purchased, net 4.8 6 6.9 12 Natural gas basis swaps purchased 6.2 24 90.1 36 Gas Utility Natural gas futures purchased 25.9 12 69.0 12 At September 30, 2020, neither Spire Missouri nor Spire Marketing had any further price mitigation in place. Derivative instruments designated as cash flow hedges of forecasted transactions are recognized on the balance sheets of the Company at fair value, and the change in fair value of the effective portion of these hedge instruments is recorded, net of income tax, in other comprehensive income or loss (OCI). Accumulated other comprehensive income or loss (AOCI) is a component of Total Common Stock Equity. Amounts are reclassified from AOCI into earnings when the hedged items affect net income, using the same revenue or expense category that the hedged item impacts. Based on market prices at September 30, 20 20 , it is expected that an immaterial amount of unrealized gains will be reclassified into the Consolidated Statements of Income of the Company during the next twelve months. Cash flows from hedging transactions are classified in the same category as the cash flows from the items that are being hedged in the Consolidated Statements of Cash Flows. Effect of Derivative Instruments on the Consolidated Statements of Income and Comprehensive Income Location of Gain (Loss) Recorded in Income 2020 2019 2018 Derivatives in Cash Flow Hedging Relationships Effective portion of gain (loss) recognized in OCI on derivatives: Interest rate swaps (8.9 ) (46.4 ) 3.9 Total $ (8.9 ) $ (46.4 ) $ 3.9 Effective portion of gain (loss) reclassified from AOCI to income: Gasoline and heating oil contracts Gas Utility Other Operating Expenses — — 0.1 Interest rate swaps Interest Expense (3.2 ) 1.3 1.4 Total $ (3.2 ) $ 1.3 $ 1.5 Derivatives Not Designated as Hedging Instruments* Gain (loss) recognized in income on derivatives: Natural gas commodity contracts Gas Marketing Operating Revenues $ 9.2 $ 2.5 $ 10.2 Gas Marketing Operating Expenses — (8.4 ) (8.1 ) NYMEX / ICE natural gas contracts Gas Marketing Operating Revenues (11.8 ) — — Total $ (2.6 ) $ (5.9 ) $ 2.1 * Gains and losses on Spire Missouri’s natural gas derivative instruments, which are not designated as hedging instruments for financial reporting purposes, are deferred pursuant to the Missouri Utilities’ PGA clauses and initially recorded as regulatory assets or regulatory liabilities. These gains and losses are excluded from the table above because they have no direct impact on the statements of income. Such amounts are recognized in the statements of income as a component of Regulated Gas Distribution Natural and Propane Gas operating expenses when they are recovered through the PGA clause and reflected in customer billings. Fair Value of Derivative Instruments in the Consolidated Balance Sheets Derivative Assets* Derivative Liabilities* September 30, 2020 Balance Sheet Location Fair Value Balance Sheet Location Fair Value Derivatives designated as hedging instruments Other: Interest rate swaps Derivative Instrument Liability $ — Derivative Instrument Liability $ 54.2 Subtotal — 54.2 Derivatives not designated as hedging instruments Gas Utility: Natural gas contracts Accounts Receivable – Other 6.3 Accounts Receivable – Other 0.9 Gasoline and heating oil contracts Derivative Instrument Assets 0.3 — Gas Marketing: NYMEX / ICE natural gas contracts Derivative Instrument Assets 20.5 Derivative Instrument Assets 21.3 Deferred Charges – Other 7.2 Deferred Charges – Other 0.8 Natural gas commodity Derivative Instrument Assets 13.5 Derivative Instrument Assets — Deferred Charges – Other 1.4 Deferred Charges – Other — Current Liabilities – Other — Current Liabilities – Other 16.8 Deferred Credits – Other — Deferred Credits – Other 5.5 Subtotal 49.2 45.3 Total derivatives $ 49.2 $ 99.5 September 30, 2019 Derivatives designated as hedging instruments Other: Interest rate swaps Derivative Instrument Liability $ — Derivative Instrument Liability $ 43.4 Subtotal — 43.4 Derivatives not designated as hedging instruments Gas Utility: Natural gas contracts Accounts Receivable – Other — Accounts Receivable – Other 12.3 Gas Marketing: NYMEX / ICE natural gas contracts Derivative Instrument Assets 7.0 Derivative Instrument Assets 7.3 Deferred Charges – Other 0.5 Deferred Charges – Other 1.6 Natural gas commodity Derivative Instrument Assets 10.4 Derivative Instrument Assets 0.9 Deferred Charges – Other 4.8 Deferred Charges – Other — Current Liabilities – Other 1.4 Current Liabilities – Other 11.5 Deferred Credits – Other 0.1 Deferred Credits – Other 1.5 Subtotal 24.2 35.1 Total derivatives $ 24.2 $ 78.5 * The fair values of Derivative Assets and Derivative Liabilities exclude the fair value of cash margin receivables or payables with counterparties subject to netting arrangements. Fair value amounts of derivative contracts (including the fair value amounts of cash margin receivables and payables) for which there is a legal right to set off are presented net on the balance sheets. As such, the gross balances presented in the table above are not indicative of the Company’s net economic exposure. Refer to Note 9 Following is a reconciliation of the amounts in the tables above to the amounts presented in the Consolidated Balance Sheets: 2020 2019 Fair value of derivative assets presented above $ 49.2 $ 24.2 Fair value of cash margin receivable offset with derivatives (9.0 ) 14.3 Netting of assets and liabilities with the same counterparty (23.0 ) (23.7 ) Total $ 17.2 $ 14.8 Derivative Instrument Assets, per Consolidated Balance Sheets: Current Assets – Other $ 15.8 $ 4.2 Deferred Charges and Other Assets – Other 1.4 10.6 Total $ 17.2 $ 14.8 Fair value of derivative liabilities presented above $ 99.5 $ 78.5 Netting of assets and liabilities with the same counterparty (23.0 ) (23.7 ) Total $ 76.5 $ 54.8 Derivative Instrument Liabilities, per Consolidated Balance Sheets: Current Liabilities – Other $ 71.0 $ 50.0 Deferred Credits and Other Liabilities – Other 5.5 4.8 Total $ 76.5 $ 54.8 Additionally, at September 30, 2020 and 2019, the Company had $7.6 and $8.1, respectively, in cash margin receivables not offset with derivatives, which are presented in Accounts Receivable – Other. Spire Missouri Spire Missouri has a risk management policy to utilize various derivatives, including futures contracts, exchange-traded options, swaps and over-the-counter instruments for the explicit purpose of managing price risk associated with purchasing and delivering natural gas on a regular basis to customers in accordance with its tariffs. The objective of this policy is to limit Spire Missouri’s exposure to natural gas price volatility and to manage, hedge and mitigate substantial price risk. This policy strictly prohibits speculation and permits Spire Missouri to hedge current physical natural gas purchase commitments or forecasted or anticipated future peak (maximum) physical need for natural gas delivered. Costs and cost reductions, including carrying costs, associated with Spire Missouri’s use of natural gas derivative instruments are allowed to be passed on to Spire Missouri customers through the operation of its PGA clause, through which the MoPSC allows Spire Missouri to recover gas supply costs, subject to prudence review by the MoPSC. Accordingly, Spire Missouri does not expect any adverse earnings impact as a result of the use of these derivative instruments. Spire Missouri does not designate these instruments as hedging instruments for financial reporting purposes because gains or losses associated with the use of these derivative instruments are deferred and recorded as regulatory assets or regulatory liabilities pursuant to ASC Topic 980, Regulated Operations The timing of the operation of the PGA clause may cause interim variations in short-term cash flows, because Spire Missouri is subject to cash margin requirements associated with changes in the values of these instruments. Nevertheless, carrying costs associated with such requirements are recovered through the PGA clause. From time to time, Spire Missouri purchases NYMEX futures and options contracts to help stabilize operating costs associated with forecasted purchases of gasoline and diesel fuels used to power vehicles and equipment used in the course of its business. These contracts are designated as cash flow hedges of forecasted transactions pursuant to ASC Topic 815, Derivatives and Hedging Derivative instruments designated as cash flow hedges of forecasted transactions are recognized on the balance sheets at fair value and the change in the fair value of the effective portion of these hedge instruments is recorded, net of income tax, in OCI. AOCI is a component of Total Common Stock Equity. Amounts are reclassified from AOCI into earnings when the hedged items affect net income, using the same revenue or expense category that the hedged item impacts. Based on market prices at September 30, 20 20 , it is expected that an immaterial amount of pre-tax gains will be reclassified into the statements of income during fiscal 20 2 1 . Cash flows from hedging transactions are classified in the same category as the cash flows from the items that are being hedged in the statements of cash flows. Spire Missouri’s derivative instruments consist primarily of NYMEX positions. The NYMEX is the primary national commodities exchange on which natural gas derivatives are traded. Open NYMEX natural gas futures positions at September 30, 2020 were as follows: September 30, 2020 Notional (MMBtu millions) Maximum Term (Months) Natural gas futures purchased 25.9 12 At September 30, 2020, Spire Missouri had no other price mitigation derivatives in place. Effect of Derivative Instruments on the Statements of Comprehensive Income Location of Gain (Loss) Recorded in Income 2020 2019 2018 Derivatives in Cash Flow Hedging Relationships Effective portion of gain (loss) recognized in OCI on derivatives: Gasoline and heating oil contracts $ — $ — $ — Effective portion of gain (loss) reclassified from AOCI to income: Gasoline and heating oil contracts Gas Utility Other Operating Expenses $ — $ — $ 0.1 * Gains and losses on Spire Missouri’s natural gas derivative instruments, which are not designated as hedging instruments for financial reporting purposes, are deferred pursuant to the Spire Missouri’s PGA clauses and initially recorded as regulatory assets or regulatory liabilities. These gains and losses are excluded from the table above because they have no direct impact on the Statements of Income. Such amounts are recognized in the Statements of Income as a component of Regulated Gas Distribution Natural and Propane Gas operating expenses when they are recovered through the PGA clause and reflected in customer billings. Fair Value of Derivative Instruments in the Balance Sheets Derivative Assets* Derivative Liabilities* September 30, 2020 Balance Sheet Location Fair Value Balance Sheet Location Fair Value Derivatives not designated as hedging instruments Natural gas contracts Accounts Receivable – Other $ 6.3 Accounts Receivable – Other $ 0.9 Gasoline and heating oil contracts Derivative Instrument Assets 0.3 — Total derivatives $ 6.6 $ 0.9 September 30, 2019 Derivatives not designated as hedging instruments Natural gas contracts Accounts Receivable – Other $ — Accounts Receivable – Other $ 12.3 * The fair values of Derivative Assets and Derivative Liabilities exclude the fair value of cash margin receivables or payables with counterparties subject to netting arrangements. Fair value amounts of derivative contracts (including the fair value amounts of cash margin receivables and payables) for which there is a legal right to set off are presented net on the Balance Sheets. As such, the gross balances presented in the table above are not indicative of Spire Missouri’s net economic exposure. Refer to Note 9 Following is a reconciliation of the amounts in the tables above to the amounts presented in Spire Missouri’s Balance Sheets: 2020 2019 Fair value of derivative assets presented above $ 6.6 $ — Fair value of cash margin (payable) receivable offset with derivatives (5.7 ) 12.3 Netting of assets and liabilities with the same counterparty (0.9 ) (12.3 ) Total $ — $ — Fair value of derivative liabilities presented above $ 0.9 $ 12.3 Netting of assets and liabilities with the same counterparty (0.9 ) (12.3 ) Total $ — $ — Additionally, at September 30, 2019 and 2018, Spire Missouri had $7.2 and $7.8, respectively, in cash margin receivables not offset with derivatives, which are presented in Accounts Receivable – Other. Spire Alabama Spire Alabama periodically employs a gasoline derivative program to help stabilize operating costs associated with forecasted purchases of gasoline and diesel fuels used to power vehicles and equipment used in the course of its business. The gains or losses on these derivative instruments are not subject to Spire Alabama’s GSA rider. The level of contracts outstanding as of September 30, 2020 and 2019 were not material.

Concentrations of Credit Risk

Concentrations of Credit Risk	12 Months Ended
	Sep. 30, 2020
Risks And Uncertainties [Abstract]
Concentrations of Credit Risk	11. CONCENTRATIONS OF CREDIT RISK Spire’s Gas Utility segment serves 1.7 million customers in three states across multiple rate classes resulting in a significant amount of revenue diversity. Credit risk is mitigated by the high percentage of residential customers as well as the geographic diversity of the Utilities, though customers for each of the Utilities are concentrated in a single state. Spire Marketing’s accounts receivable attributable to utility companies and their marketing affiliates totaled $73.0 at September 30, 2020. The concentration of transactions with these counterparties has the potential to affect the Company’s overall exposure to credit risk, either positively or negatively, in that customers in this group may be affected similarly by changes in economic, industry, or other conditions. Spire Marketing also has concentrations of credit risk with certain individually significant counterparties. At September 30, 2020, the amounts included in accounts receivable from its five largest counterparties (in terms of net accounts receivable exposure) totaled $35.7. Four To manage these risks, Spire Marketing has established procedures to determine the creditworthiness of its counterparties. These procedures include obtaining credit ratings and credit reports, analyzing counterparty financial statements to assess financial condition, and considering the industry environment in which the counterparty operates. This information is monitored on an ongoing basis. In some instances, Spire Marketing may require credit assurances such as prepayments, letters of credit, or parental guaranties. In addition, Spire Marketing may enter into netting arrangements to mitigate credit risk with counterparties in the energy industry with whom it conducts both sales and purchases of natural gas. Where there is no netting arrangement, Spire Marketing records accounts receivable, accounts payable, and prepayments for physical sales and purchases of natural gas on a gross basis. Sales are typically made on an unsecured credit basis with payment due the month following delivery. Accounts receivable amounts are closely monitored and provisions for uncollectible amounts are accrued when losses are probable.

Income Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	12. INCOME TAXES The Company, Spire Missouri, and Spire Alabama are subject to federal income tax as well as income tax in various state and local jurisdictions. Spire files a consolidated federal income tax return and various state income tax returns and allocates income taxes to Spire Missouri, Spire Alabama and its other subsidiaries as if each entity were a separate taxpayer. The provision (benefit) for income taxes during the fiscal years ended September 30, 2020, 2019, and 2018 was as follows: Spire Spire Missouri Spire Alabama 2020 2019 2018 2020 2019 2018 2020 2019 2018 Federal: Current $ 0.4 $ 0.6 $ — $ — $ — $ — $ — $ — $ — Deferred 5.8 27.4 (22.7 ) 14.9 11.5 (26.1 ) 17.4 16.3 81.5 Investment tax credits (0.2 ) (0.2 ) (0.2 ) (0.2 ) (0.2 ) (0.2 ) — — — State and local: Current 3.0 2.1 2.2 0.1 — — — — — Deferred 3.4 4.6 (5.8 ) 2.5 2.0 (6.3 ) 4.6 4.2 0.1 Total income tax expense (benefit) $ 12.4 $ 34.5 $ (26.5 ) $ 17.3 $ 13.3 $ (32.6 ) $ 22.0 $ 20.5 $ 81.6 The effective income tax rate varied from the federal statutory income tax rate for each year due to the following: Spire Spire Missouri Spire Alabama 2020 2019 2018 2020 2019 2018 2020 2019 2018 Federal income tax statutory rate 21.0 % 21.0 % 24.5 % 21.0 % 21.0 % 24.5 % 21.0 % 21.0 % 24.5 % State and local income taxes, net of federal income tax benefits 9.0 3.6 3.4 2.6 2.6 3.4 4.1 4.1 3.8 Certain expenses capitalized on books and deducted on tax return (6.6 ) (3.8 ) (2.3 ) (4.6 ) (6.5 ) (4.6 ) — — — Taxes related to prior years (1.8 ) 0.2 (0.4 ) (1.4 ) 0.1 (0.7 ) 0.1 — — Tax law changes — — (35.9 ) — — (50.3 ) — — 70.0 Amortization of excess deferred taxes (8.3 ) (3.8 ) (1.8 ) (5.7 ) (6.6 ) (3.6 ) — — — Other items – net * (1.0 ) (1.4 ) (1.6 ) (0.2 ) (0.3 ) (2.5 ) (0.1 ) 0.2 0.1 Effective income tax rate 12.3 % 15.8 % (14.1 )% 11.7 % 10.3 % (33.8 )% 25.1 % 25.3 % 98.4 % * Other consists primarily of property adjustments. The significant items comprising the net deferred tax liability or asset as of September 30 were as follows: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Deferred tax assets: Reserves not currently deductible $ 24.8 $ 31.4 $ 16.7 $ 21.2 $ 5.9 $ 6.2 Pension and other postretirement benefits 108.3 102.7 78.5 78.7 — — Goodwill — — — — 101.3 116.8 Operating losses 170.4 162.2 36.0 51.1 111.3 94.2 Regulatory amount due to customers, net 36.1 46.5 32.3 42.7 — — Other 44.7 20.0 — 1.2 — — Deferred tax assets 384.3 362.8 163.5 194.9 218.5 217.2 Less: Valuation allowance (0.9 ) (1.8 ) (0.9 ) (1.8 ) — — Total deferred tax assets 383.4 361.0 162.6 193.1 218.5 217.2 Deferred tax liabilities: Relating to property (614.0 ) (562.9 ) (427.1 ) (395.1 ) (151.4 ) (129.3 ) Regulatory pension and other postretirement benefits (138.4 ) (135.9 ) (107.4 ) (111.7 ) (3.4 ) (2.0 ) Other** (142.4 ) (113.6 ) (62.8 ) (50.9 ) (4.4 ) (4.6 ) Total deferred tax liabilities (894.8 ) (812.4 ) (597.3 ) (557.7 ) (159.2 ) (135.9 ) Net deferred tax (liability) asset $ (511.4 ) $ (451.4 ) $ (434.7 ) $ (364.6 ) $ 59.3 $ 81.3 ** For Spire, Other consists primarily of goodwill-related liabilities. The Tax Cuts and Jobs Act (TCJA) was signed into law on December 22, 2017, with an effective date of January 1, 2018, for substantially all of the provisions. This comprehensive act includes significant reform of the current income tax code including changes in the calculation for business entities and a reduction in the corporate federal income tax rate from 35% to 21%. The specific provisions related to regulated public utilities in the TCJA generally allow for the continued deductibility of interest expense, the elimination of full expensing for tax purposes of certain property acquired after September 27, 2017 and the continuation of certain rate normalization requirements for accelerated depreciation benefits. ASC Topic 740, Income Taxes, As indicated in Note 1 Regulated Operations The Company recorded the TCJA impacts in fiscal 2018, including the impact of the federal income tax rate reduction and the revaluation of the deferred tax assets and liabilities . The total adjustments recorded, before reduction for amounts returned to customers, for the year ended September 30, 2018, were as follows: Spire Spire Missouri Spire Alabama Adjustment to deferred tax liabilities $ (318.3 ) $ (285.3 ) $ (61.0 ) Adjustment to deferred income tax expense (75.0 ) (57.0 ) 58.8 Adjustment to regulatory assets (75.9 ) (78.1 ) 2.2 Adjustment to regulatory liabilities 167.4 150.2 — In assessing whether deferred tax assets are realizable, management considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. Management considers all significant available positive and negative evidence, including the existence of losses in recent years, the timing of deferred tax liability reversals, projected future taxable income, taxable income in carryback years, and tax planning strategies to assess the need for a valuation allowance. Based upon this evidence, management believes it is more likely than not the Company, Spire Missouri and Spire Alabama will realize the benefits of these deferred tax assets, except for the contribution carryforward valuation allowances noted below. The Company had federal and state loss carryforwards of approximately $726.8 Spire Missouri had federal and state loss carryforwards of approximately $207.8 at September 30, 2020 on a separate company basis, which begin to expire in fiscal 2035. For federal tax purposes, these loss carryforwards may be utilized against income from another member of the consolidated group. Spire Missouri also has contribution carryforwards of approximately $5.4 at September 30, 2020 that began to expire this year. Spire Missouri has a valuation allowance of $3.0, as a portion of the contribution carryforward will not be realized prior to its expiration. Spire Missouri also has approximately $2.0 On a separate company basis, Spire Alabama had federal and state loss carryforwards of approximately $443.5 at September 30, 2020. The loss carryforwards begin to expire in fiscal 2030 for state purposes and fiscal 2035 for federal purposes. For federal tax purposes, these loss carryforwards may be utilized against income from another member of the consolidated group. The Company, Spire Missouri and Spire Alabama recognize the tax benefit from a tax position only if it is at least more likely than not that the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. Unrecognized tax benefits are reported as a reduction of a deferred tax asset for an operating loss carryforward to the extent the recognition of the benefit would impact the operating loss carryforward, pursuant to ASU 2013-11. In addition, pursuant to the TCJA, the deferred tax asset for a net operating loss carryforward was revalued in fiscal 2018 based on the federal tax law change. The following table presents a reconciliation of the beginning and ending balances of unrecognized tax benefits: Spire Spire Missouri 2020 2019 2018 2020 2019 2018 Unrecognized tax benefits, beginning of year $ 10.7 $ 8.1 $ 11.0 $ 10.4 $ 7.8 $ 10.7 Decrease related to tax law changes — — (4.0 ) — — (4.0 ) Increases related to tax positions taken in current year 2.6 4.5 1.2 2.6 4.5 1.1 Reductions related to tax positions taken in prior year — (1.9 ) — — (1.9 ) — Reductions due to lapse of applicable statute of limitations (0.1 ) — (0.1 ) — — — Unrecognized tax benefits, end of year $ 13.2 $ 10.7 $ 8.1 $ 13.0 $ 10.4 $ 7.8 As of September 30, 2020 and 2019, the amounts of unrecognized tax benefits which, if recognized, would affect the effective tax rate were $2.9 and $2.5 The Company, Spire Missouri, and Spire Alabama record potential interest and penalties related to uncertain tax positions as interest expense and other income deductions, respectively. As of September 30, 2020 and 2019, interest accrued associated with uncertain tax positions was de minimis, and no penalties were accrued. The Company, Spire Missouri, and Spire Alabama are no longer subject to examination for fiscal years prior to 2017, except to the extent the net operating losses from prior years are reviewed.

Pension Plans and Other Postret

Pension Plans and Other Postretirement Benefits	12 Months Ended
	Sep. 30, 2020
Compensation And Retirement Disclosure [Abstract]
Pension Plans and Other Postretirement Benefits	13. PENSION PLANS AND OTHER POSTRETIREMENT BENEFITS Pension Plans The pension plans of Spire consist of plans for employees at Spire Missouri, the employees of Spire Alabama and employees of the subsidiaries of Spire EnergySouth. Spire Missouri has non-contributory, defined benefit, trusteed forms of pension plans covering the majority of their employees. Plan assets consist primarily of corporate and U.S. government obligations and a growth segment consisting of exposure to equity markets, commodities, real estate and inflation-indexed securities, achieved through derivative instruments. Spire Alabama has non-contributory, defined benefit, trusteed forms of pension plans covering the majority of its employees. Qualified plan assets are comprised of mutual and commingled funds consisting of U.S. equities with varying strategies, global equities, alternative investments, and fixed income investments. The net periodic pension costs include the following components: Spire Spire Missouri Spire Alabama 2020 2019 2018 2020 2019 2018 2020 2019 2018 Service cost – benefits earned during the period $ 22.5 $ 19.3 $ 20.2 $ 15.7 $ 12.4 $ 12.7 $ 6.1 $ 6.2 $ 6.4 Interest cost on projected benefit obligation 22.6 28.2 27.4 15.8 19.8 19.5 4.9 6.0 5.5 Expected return on plan assets (35.0 ) (36.3 ) (37.0 ) (24.6 ) (25.5 ) (27.2 ) (6.9 ) (7.3 ) (6.5 ) Amortization of prior service (credit) cost (2.5 ) (1.1 ) (0.9 ) 0.1 0.9 0.9 (2.4 ) (1.8 ) (1.8 ) Amortization of actuarial loss 14.4 9.3 10.9 11.3 8.7 9.4 3.1 0.8 1.5 Loss on lump-sum settlements and curtailments 31.6 — 18.6 26.6 — 16.1 5.0 — 2.4 Subtotal 53.6 19.4 39.2 44.9 16.3 31.4 9.8 3.9 7.5 Regulatory adjustment 6.6 39.6 37.4 3.9 31.8 32.1 1.8 6.9 4.5 Net pension cost $ 60.2 $ 59.0 $ 76.6 $ 48.8 $ 48.1 $ 63.5 $ 11.6 $ 10.8 $ 12.0 Other changes in plan assets and pension benefit obligations recognized in other comprehensive income or loss include the following: Spire Spire Missouri Spire Alabama 2020 2019 2018 2020 2019 2018 2020 2019 2018 Current year actuarial loss (gain) $ 68.0 $ 90.9 $ (1.4 ) $ 37.8 $ 59.0 $ 2.2 $ 24.4 $ 26.3 $ (0.6 ) Amortization of actuarial loss (14.4 ) (9.3 ) (10.9 ) (11.3 ) (8.7 ) (9.4 ) (3.1 ) (0.8 ) (1.5 ) Acceleration of loss recognized due to settlement (31.7 ) — (18.5 ) (26.6 ) — (16.1 ) (5.1 ) — (2.4 ) Current year service credit (4.4 ) (10.2 ) (0.1 ) (4.4 ) (3.7 ) — — (6.5 ) — Transfer due to merger — — 0.1 — — 0.1 — — — Amortization of prior service credit (cost) 2.5 1.1 (2.9 ) (0.1 ) (0.9 ) (0.9 ) 2.4 1.8 — Amortization of transition asset — — 1.8 — — — — — 1.8 Subtotal 20.0 72.5 (31.9 ) (4.6 ) 45.7 (24.1 ) 18.6 20.8 (2.7 ) Regulatory adjustment (19.5 ) (71.7 ) 31.6 5.1 (44.9 ) 23.8 (18.6 ) (20.8 ) 2.7 Total recognized in OCI $ 0.5 $ 0.8 $ (0.3 ) $ 0.5 $ 0.8 $ (0.3 ) $ — $ — $ — Spire pension obligations are driven by separate plan and regulatory provisions governing Spire Missouri, Spire Alabama and Spire EnergySouth pension plans. Pursuant to the provisions of Spire Missouri’s and Spire Alabama’s pension plans, pension obligations may be satisfied by monthly annuities, lump-sum cash payments, or special termination benefits. Lump-sum payments are recognized as settlements (which can result in gains or losses) only if the total of such payments exceeds the sum of service and interest costs in a specific year. Special termination benefits, when offered, are also recognized as settlements which can result in gains or losses. In the fiscal year ended September 30, 2020, two Spire Missouri plans and one Spire Alabama plan met the criteria for settlement recognition, requiring re-measurement of the obligation under those plans using updated census data and assumptions for discount rate and mortality. For the remeasurements, the discount rates for the Missouri plans were updated to 2.85% at September 30, 2020 (from 3.2% at September 30, 2019), and the discount rate for the Alabama plan was updated to 2.95% (from 3.20%). No Spire plans met the criteria for settlement recognition for the fiscal year ended September 30, 2019. Pursuant to a MoPSC Order, the return on plan assets is based on the market-related value of plan assets implemented prospectively over a four-year Effective April 19, 2018, the pension cost for Spire Missouri’s western territory (Missouri West) included in customer rates was reduced from $9.9 to $5.5 per year, the pension cost included in Spire Missouri’s eastern territory (Missouri East) customer rates was increased from $15.5 to $29.0 per year. Over an amortization period of eight years, Missouri East rates also include the amortization of $173.0 of assets for pension and other postretirement benefits, and Missouri West rates will be reduced by the amortization of a $26.2 net liability for pension and other postretirement benefits. The difference between these amounts and pension expense as calculated pursuant to the above and that otherwise would be included in the statements of income and statements of comprehensive income is deferred as a regulatory asset or regulatory liability. The following table shows the reconciliation of the beginning and ending balances of the pension benefit obligation at September 30: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Benefit obligation, beginning of year $ 751.4 $ 664.6 $ 538.4 $ 473.3 $ 152.5 $ 136.3 Service cost 22.5 19.3 15.7 12.4 6.1 6.2 Interest cost 22.6 28.2 15.8 19.8 4.9 6.0 Actuarial loss (gain) 37.5 104.8 15.6 76.0 18.4 23.7 Plan amendments (4.4 ) (10.2 ) (4.4 ) (3.7 ) — (6.5 ) Settlement loss 16.5 — 16.5 — — — Settlement benefits paid (89.3 ) — (74.5 ) — (14.8 ) — Regular benefits paid (24.2 ) (55.3 ) (17.9 ) (39.4 ) (3.6 ) (13.2 ) Benefit obligation, end of year $ 732.6 $ 751.4 $ 505.2 $ 538.4 $ 163.5 $ 152.5 Accumulated benefit obligation, end of year $ 699.3 $ 712.9 $ 473.7 $ 500.2 $ 161.8 $ 152.3 The following table sets forth the reconciliation of the beginning and ending balances of the fair value of plan assets at September 30: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Fair value of plan assets, beginning of year $ 521.8 $ 499.2 $ 379.2 $ 349.1 $ 93.3 $ 101.3 Actual return on plan assets 21.1 50.1 19.1 42.4 1.0 4.7 Employer contributions 43.7 27.8 30.3 27.1 12.7 0.5 Settlement benefits paid (89.3 ) — (74.5 ) — (14.8 ) — Regular benefits paid (24.2 ) (55.3 ) (17.9 ) (39.4 ) (3.6 ) (13.2 ) Fair value of plan assets, end of year $ 473.1 $ 521.8 $ 336.2 $ 379.2 $ 88.6 $ 93.3 Funded status of plans, end of year $ (259.5 ) $ (229.6 ) $ (169.0 ) $ (159.2 ) $ (74.9 ) $ (59.2 ) The following table sets forth the amounts recognized in the balance sheets at September 30: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Current liabilities $ (0.6 ) $ (0.5 ) $ (0.6 ) $ (0.5 ) $ — $ — Noncurrent liabilities (258.9 ) (229.1 ) (168.4 ) (158.7 ) (74.9 ) (59.2 ) Total $ (259.5 ) $ (229.6 ) $ (169.0 ) $ (159.2 ) $ (74.9 ) $ (59.2 ) Pre-tax amounts recognized in accumulated other comprehensive loss not yet recognized as components of net periodic pension cost consist of: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Net actuarial loss $ 235.6 $ 213.7 $ 152.9 $ 153.1 $ 78.1 $ 61.9 Prior service (credit) cost (25.6 ) (23.7 ) (2.8 ) 1.7 (21.1 ) (23.5 ) Subtotal 210.0 190.0 150.1 154.8 57.0 38.4 Adjustments for amounts included in regulatory assets (206.7 ) (187.1 ) (146.8 ) (151.9 ) (57.0 ) (38.4 ) Total $ 3.3 $ 2.9 $ 3.3 $ 2.9 $ — $ — At September 30, 2020, the following pre-tax amounts are expected to be amortized from accumulated other comprehensive loss into net periodic pension cost during fiscal 2020: Spire Spire Missouri Spire Alabama Amortization of net actuarial loss $ 16.0 $ 11.4 $ 4.6 Amortization of prior service (credit) cost (3.2 ) (0.6 ) (2.4 ) Subtotal 12.8 10.8 2.2 Regulatory adjustment (12.5 ) (10.5 ) (2.2 ) Total $ 0.3 $ 0.3 $ — The assumptions used to calculate net periodic pension costs for Spire Missouri are as follows: 2020 2019 2018 Weighted average discount rate - Spire Missouri East plan 3.20% 4.30% 3.75% Weighted average discount rate - Spire Missouri West plan 3.15% 4.35% 3.70% Weighted average rate of future compensation increase 3.00% 3.00% 3.00% Expected long-term rate of return on plan assets 7.25% 7.50% 7.75% The assumptions used to calculate net periodic pension costs for Spire Alabama are as follows: 2020 2019 2018 Weighted average discount rate 3.25%/3.20% 4.35% 3.65%/3.70% Weighted average rate of future compensation increase 3.00% 3.00% 3.00% Expected long-term rate of return on plan assets 7.25% 7.25% 7.25% The discount rate is based on long-term, high quality bond indices at the measurement date. The expected long-term rate of return on plan assets is based on historical and projected rates of return for current and planned asset classes in the investment portfolio. Assumed projected rates of return for each asset class were selected after analyzing historical experience and future expectations of the returns. The overall expected rate of return for the portfolio was developed based on the target allocation for each class. The assumptions used to calculate the benefit obligations are as follows: 2020 2019 Weighted average discount rate - Spire Missouri East plan 2.85% 3.20% Weighted average discount rate - Spire Missouri West plan 2.75% 3.15% Weighted average discount rate - Spire Alabama plans 2.95%/2.80% 3.20%/3.25% Weighted average rate of future compensation increase 3.00% 3.00% Following are the year-end projected benefit obligation, accumulated benefit obligation, and fair value of plan assets for plans that have a projected benefit obligation and an accumulated benefit obligation in excess of plan assets: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Projected benefit obligation $ 732.6 $ 751.4 $ 505.2 $ 538.4 $ 163.5 $ 152.5 Accumulated benefit obligation 699.3 712.9 473.7 500.2 161.8 152.3 Fair value of plan assets 473.1 521.8 336.2 379.2 88.6 93.3 Following are the targeted and actual plan assets by category as of September 30 of each year for Spire Missouri and Spire Alabama: Spire Missouri 2020 Target 2020 Actual 2019 Target 2019 Actual Return seeking assets 70.0 % 70.0 % 56.5 % 57.0 % Liability hedging assets 30.0 % 27.0 % 43.5 % 39.8 % Other — % 3.0 % — % 3.2 % Total 100.0 % 100.0 % 100.0 % 100.0 % Spire Alabama 2020 Target 2020 Actual 2019 Target 2019 Actual Return seeking assets 70.0 % 71.0 % 60.0 % 58.5 % Liability hedging assets 30.0 % 27.0 % 29.0 % 29.8 % Other* — 2.0 % 11.0 % 11.7 % Total 100.0 % 100.0 % 100.0 % 100.0 % * Includes cash for 2020. For 2019, includes cash and funds invested in real estate, commodities, natural resources and inflation-protected securities. Spire Missouri’s investment policies are designed to maximize, to the extent possible, the funded status of the plans over time, and minimize volatility of funding and costs. The policy seeks to maximize investment returns consistent with these objectives and Spire Missouri’s tolerance for risk. The duration of plan liabilities and the impact of potential changes in asset values on the funded status are fundamental considerations in the selection of plan assets. Outside investment management specialists are utilized in each asset class. Such specialists are provided with guidelines, where appropriate, designed to ensure that the investment portfolio is managed in accordance with the policy. The policy seeks to avoid significant concentrations of risk by investing in a diversified portfolio of assets, currently including a growth (equity) component and a liability-driven (debt) component. Investments in corporate, U.S. government and agencies, and, to a lesser extent, international debt securities seek to provide duration matching with plan liabilities, and typically have investment grade ratings and reflect allocations across various entities and industries. There are also exposures to additional asset types in the target portfolio: commodities, real estate and inflation-indexed securities. For the Missouri East plan, the investment policy permits the use of derivative instruments, which may be used to achieve the desired market exposure of an index, adjust portfolio duration, or rebalance the total portfolio to the target asset allocation. The growth strategy utilizes a combination of derivative instruments and debt securities to achieve diversified exposure to equity and other markets while generating returns from the fixed-income investments and providing further duration matching with the liabilities. Performance and compliance with the guidelines are regularly monitored. The policy calls for increased allocations to debt securities as the funded status improves. Spire Alabama employs a total return investment approach whereby a mix of equities and fixed income investments are used to maximize the long-term return of plan assets with a prudent level of risk. Risk tolerance is established through consideration of plan liabilities, plan funded status, corporate financial condition and market conditions. Spire Alabama has developed an investment strategy that focuses on asset allocation, diversification and quality guidelines. The investment goals are to obtain an adequate level of return to meet future obligations of the plans by providing above average risk-adjusted returns with a risk exposure in the mid-range of comparable funds. Investment managers are retained by Spire Alabama to manage separate pools of assets. Funds are allocated to such managers in order to achieve an appropriate, diversified, and balanced asset mix. Comparative market and peer group benchmarks are utilized to ensure that investment managers are performing satisfactorily. Spire Alabama seeks to maintain an appropriate level of diversification to minimize the risk of large losses in a single asset class. Accordingly, plan assets for the pension plans do not have a concentration of assets in a single entity, industry, country, commodity or class of investment fund. Following are expected pension benefit payments for the succeeding five fiscal years, and in aggregate for the five fiscal years thereafter, for Spire, Spire Missouri, and Spire Alabama: 2021 2022 2023 2024 2025 2026- 2030 Spire $ 65.6 $ 64.1 $ 60.8 $ 58.6 $ 54.4 $ 246.0 Spire Missouri 49.1 45.6 43.3 41.9 37.7 168.7 Spire Alabama 13.5 15.4 14.3 13.5 13.3 59.0 The funding policy of Spire Missouri and Spire Alabama is to contribute an amount not less than the minimum required by government funding standards nor more than the maximum deductible amount for federal income tax purposes. Spire Missouri’s contributions to the pension plans in fiscal 2021 are anticipated to be $36.4 into the qualified trusts, and $0.6 into the non-qualified plans. Spire Alabama’s contributions to the pension plans in fiscal 2021 are anticipated to be $11.3 into the qualified trusts. Other Postretirement Benefits Spire and the Utilities provide certain life insurance benefits at retirement. Spire Missouri plans provide for medical insurance after early retirement until age 65. For retirements prior to January 1, 2015, the Missouri West plans provided medical insurance after retirement until death. The Spire Alabama plans provide medical insurance upon retirement until death for certain retirees depending on the type of employee and the date the employee was originally hired. Net periodic postretirement benefit costs consist of the following components: Spire Spire Missouri Spire Alabama 2020 2019 2018 2020 2019 2018 2020 2019 2018 Service cost – benefits earned during the period $ 5.9 $ 7.4 $ 9.4 $ 5.3 $ 6.8 $ 9.0 $ 0.4 $ 0.4 $ 0.2 Interest cost on accumulated postretirement benefit obligation 6.3 9.0 8.6 4.7 6.9 6.9 1.4 1.8 1.5 Expected return on plan assets (16.7 ) (16.2 ) (13.9 ) (11.4 ) (11.1 ) (9.6 ) (5.0 ) (4.8 ) (4.1 ) Amortization of prior service (credit) cost (0.5 ) (0.1 ) (0.1 ) (0.2 ) 0.3 0.3 (0.3 ) (0.4 ) (0.4 ) Amortization of actuarial (gain) loss (2.0 ) (0.5 ) 0.8 (2.0 ) (0.5 ) 0.9 — — (0.1 ) Subtotal (7.0 ) (0.4 ) 4.8 (3.6 ) 2.4 7.5 (3.5 ) (3.0 ) (2.9 ) Regulatory adjustment 16.0 10.0 2.2 17.7 11.7 3.9 (1.8 ) (1.8 ) (1.8 ) Net postretirement benefit cost $ 9.0 $ 9.6 $ 7.0 $ 14.1 $ 14.1 $ 11.4 $ (5.3 ) $ (4.8 ) $ (4.7 ) Other changes in plan assets and postretirement benefit obligations recognized in OCI include the following: Spire Spire Missouri Spire Alabama 2020 2019 2018 2020 2019 2018 2020 2019 2018 Current year actuarial (gain) loss $ (7.3 ) $ (12.2 ) $ (45.1 ) $ (7.6 ) $ (17.3 ) $ (47.1 ) $ 1.1 $ 5.5 $ 1.6 Amortization of actuarial gain (loss) 2.0 0.5 (0.8 ) 2.0 0.5 (0.9 ) — — 0.1 Current year prior service credit (cost) 15.8 5.5 — 9.5 4.9 — 6.3 0.6 — Amortization of current year service cost — 0.4 — — — — — 0.4 — Amortization of prior service (cost) credit 0.5 (0.3 ) 0.1 0.2 (0.3 ) (0.3 ) 0.3 — 0.4 Subtotal 11.0 (6.1 ) (45.8 ) 4.1 (12.2 ) (48.3 ) 7.7 6.5 2.1 Regulatory adjustment (11.0 ) 6.1 45.8 (4.1 ) 12.2 48.3 (7.7 ) (6.5 ) (2.1 ) Total recognized in OCI $ — $ — $ — $ — $ — $ — $ — $ — $ — Pursuant to a MoPSC Order, the return on plan assets is based on the market-related value of plan assets implemented prospectively over a four-year The following table sets forth the reconciliation of the beginning and ending balances of the postretirement benefit obligation at September 30: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Benefit obligation, beginning of year $ 197.3 $ 208.1 $ 147.9 $ 158.8 $ 43.4 $ 43.1 Service cost 5.9 7.4 5.3 6.8 0.4 0.4 Interest cost 6.3 9.0 4.7 6.9 1.4 1.8 Actuarial (gain) loss 0.2 (18.9 ) 1.7 (19.5 ) (0.7 ) 1.2 Plan amendments 15.8 5.5 9.5 4.9 6.3 0.6 Retiree drug subsidy program — 0.2 — 0.2 — — Benefits paid (13.2 ) (14.0 ) (10.7 ) (10.2 ) (2.5 ) (3.7 ) Benefit obligation, end of year $ 212.3 $ 197.3 $ 158.4 $ 147.9 $ 48.3 $ 43.4 The following table sets forth the reconciliation of the beginning and ending balances of the fair value of plan assets at September 30: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Fair value of plan assets at beginning of year $ 279.8 $ 283.5 $ 188.9 $ 189.5 $ 86.4 $ 89.6 Actual return on plan assets 24.2 9.7 20.8 9.0 3.1 0.5 Employer contributions 0.2 0.6 0.2 0.6 — — Benefits paid (13.2 ) (14.0 ) (10.7 ) (10.2 ) (2.5 ) (3.7 ) Fair value of plan assets, end of year $ 291.0 $ 279.8 $ 199.2 $ 188.9 $ 87.0 $ 86.4 Funded status of plans, end of year $ 78.7 $ 82.5 $ 40.8 $ 41.0 $ 38.7 $ 43.0 The following table sets forth the amounts recognized in the balance sheets at September 30: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Noncurrent assets $ 129.0 $ 118.3 $ 90.3 $ 75.3 $ 38.7 $ 43.0 Current liabilities (0.5 ) (0.5 ) (0.5 ) (0.5 ) — — Noncurrent liabilities (49.8 ) (35.3 ) (49.0 ) (33.8 ) — — Total $ 78.7 $ 82.5 $ 40.8 $ 41.0 $ 38.7 $ 43.0 Pre-tax amounts recognized in accumulated other comprehensive loss not yet recognized as components of net periodic postretirement benefit cost consist of: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Net actuarial gain $ (61.7 ) $ (56.3 ) $ (58.3 ) $ (52.6 ) $ (1.5 ) $ (2.6 ) Prior service (credit) cost 15.5 (1.0 ) 10.4 0.6 5.1 (1.6 ) Subtotal (46.2 ) (57.3 ) (47.9 ) (52.0 ) 3.6 (4.2 ) Adjustments for amounts included in regulatory assets 46.2 57.3 47.9 52.0 (3.6 ) 4.2 Total $ — $ — $ — $ — $ — $ — At September 30, 2020, the following pre-tax amounts are expected to be amortized from accumulated other comprehensive loss into net periodic postretirement benefit cost during fiscal 2020: Spire Spire Missouri Spire Alabama Amortization of net actuarial gain $ (1.6 ) $ (1.5 ) $ — Amortization of prior service credit 1.0 0.7 0.3 Subtotal (0.6 ) (0.8 ) 0.3 Regulatory adjustment 0.6 0.8 (0.3 ) Total $ — $ — $ — The assumptions used to calculate net periodic postretirement benefit costs for Spire Missouri are as follows: 2020 2019 2018 Weighted average discount rate - Spire Missouri plans 3.15% 4.30% 3.60% Weighted average rate of future compensation increase 3.00% 3.00% 3.00% Expected long-term rate of return on plan assets - Spire Missouri plans 6.25% 6.25% 5.75%/7.75% The assumptions used to calculate net periodic postretirement benefit costs for Spire Alabama are as follows: 2020 2019 2018 Weighted average discount rate 3.15% 4.30% 3.80% Expected long-term rate of return on plan assets 5.00%/6.25% 5.00%/6.25% 3.75%/6.00% The discount rate is based on long-term, high quality bond indices at the measurement date. The expected long-term rate of return on plan assets is based on historical and projected rates of return for current and planned asset classes in the investment portfolio. Assumed projected rates of return for each asset class were selected after analyzing historical experience and future expectations of the returns. The overall expected rate of return for the portfolio was developed based on the target allocation for each class. The assumptions used to calculate the accumulated postretirement benefit obligations are as follows: 2020 2019 Weighted average discount rate - Spire Alabama plans 2.75% 3.15% Weighted average discount rate - Spire Missouri plans 2.75% 3.15% Weighted average rate of future compensation increase - Spire Missouri East plans 3.00% 3.00% The assumed medical cost trend rates at September 30 are as follows: 2020 2019 Medical cost trend assumed for next year - Spire Missouri 6.50% 6.75% Medical cost trend assumed for next year - Spire Alabama 6.50% 6.75% Rate to which the medical cost trend rate is assumed to decline (the ultimate medical cost trend rate) 5.00% 5.00% Year the rate reaches the ultimate trend 2025 2025 The following table presents the effects of an assumed 1% change in the assumed medical cost trend rate: Spire Spire Missouri Spire Alabama 1% Increase 1% Decrease 1% Increase 1% Decrease 1% Increase 1% Decrease Net periodic postretirement benefit cost $ 0.8 $ (0.7 ) $ 0.6 $ (0.6 ) $ 0.2 $ (0.1 ) Accumulated postretirement benefit obligation 9.7 (8.7 ) 6.5 (5.9 ) 2.6 (2.3 ) Following are the targeted and actual plan assets by category as of September 30 of each year for Spire Missouri and Spire Alabama: Spire Missouri Target 2020 Actual 2019 Actual Equity securities 60.0 % 57.4 % 58.4 % Debt securities 40.0 % 37.8 % 38.8 % Other (cash and cash equivalents held to make benefit payments) — % 4.8 % 2.8 % Total 100.0 % 100.0 % 100.0 % Spire Alabama Target 2020 Actual 2019 Actual Equity securities 60.0 % 61.8 % 60.3 % Debt securities 40.0 % 38.2 % 39.7 % Total 100.0 % 100.0 % 100.0 % Missouri and Alabama state laws provide for the recovery in rates of costs accrued pursuant to GAAP provided that such costs are funded through an independent, external funding mechanism. The Utilities have established Voluntary Employees’ Beneficiary Association and Rabbi Trusts as external funding mechanisms. Their investment policies seek to maximize investment returns consistent with their tolerance for risk. Outside investment management specialists are utilized in each asset class. Such specialists are provided with guidelines, where appropriate, designed to ensure that the investment portfolio is managed in accordance with policy. Performance and compliance with the guidelines is regularly monitored. Spire Missouri and Spire Alabama currently invest in mutual funds which are rebalanced periodically to the target allocation. The mutual funds are diversified across U.S. stock and bond markets, and for Spire Alabama, international stock markets. Following are expected postretirement benefit payments for the succeeding five fiscal years, and in aggregate for the five fiscal years thereafter for Spire, Spire Missouri, and Spire Alabama: 2021 2022 2023 2024 2025 2026- 2030 Spire $ 14.7 $ 15.4 $ 16.1 $ 16.5 $ 16.6 $ 78.2 Spire Missouri 11.7 12.3 12.9 13.2 13.3 61.7 Spire Alabama 2.7 2.8 2.9 3.0 3.0 14.2 The Utilities’ funding policy is to contribute amounts to the trusts equal to the periodic benefit cost calculated pursuant to GAAP as recovered in rates. For Spire Missouri, contributions to the postretirement plans in fiscal 2021 are anticipated to be $4.8 to the qualified trusts and $0.6 paid directly to participants from Spire Missouri funds. It is not anticipated that contributions will be made to the Spire Alabama postretirement plans in fiscal 2021. Other Plans Spire Services Inc. sponsors a 401(k) plan that cover substantially all employees of Spire Inc. and its subsidiaries. The plan allows employees to contribute a portion of their base pay in accordance with specific guidelines. The cost of the defined contribution plan for Spire Inc. totaled $13.6, $13.8, and $12.5 for fiscal years 2020, 2019, and 2018, respectively. Spire Missouri provides a match of such contributions within specific limits. The cost of the defined contribution plan for Spire Missouri amounted to $9.5, $10.0, and $9.0 for fiscal years 2020, 2019, and 2018, respectively. Spire Alabama also provides a match of employee contributions within specific limits. The cost of the defined contribution plan for Spire Alabama amounted to $3.4 , $3.1, and $3.0 for fiscal years 2020, 2019, and 2018, respectively. Fair Value Measurements of Pension and Other Postretirement Plan Assets Spire The table below categorizes the fair value measurements of the Spire pension plan assets: Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total As of September 30, 2020 Cash and cash equivalents $ 11.5 $ — $ — $ 11.5 Equity funds - global (including U.S.) 31.4 195.6 — 227.0 Equity index funds - global (including U.S.) 32.6 — — 32.6 Debt securities: U.S. bond funds 48.9 — — 48.9 U.S. government index funds 78.3 — — 78.3 Global funds (including U.S.) — 74.8 — 74.8 Total $ 202.7 $ 270.4 $ — $ 473.1 As of September 30, 2019 Cash and cash equivalents $ 42.5 $ — $ — $ 42.5 Equity mutual funds - U.S. 40.5 17.0 — 57.5 Equity mutual funds - international 30.1 8.6 — 38.7 Debt securities: U.S. bond mutual funds 34.8 73.9 — 108.7 U.S. government 52.9 9.5 — 62.4 U.S. corporate 143.7 — — 143.7 U.S. municipal 4.0 — — 4.0 International 44.1 7.5 — 51.6 Derivatives and margin receivable 0.2 — — 0.2 103-12 Direct Filing Entities — 12.5 — 12.5 Total $ 392.8 $ 129.0 $ — $ 521.8 The table below categorizes the fair value measurements of Spire’s postretirement plan assets: Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total As of September 30, 2020 Cash and cash equivalents $ 3.6 $ — $ — $ 3.6 U.S. stock/bond mutual funds 199.4 72.2 — 271.6 International fund 1.0 14.8 — 15.8 Total $ 204.0 $ 87.0 $ — $ 291.0 As of September 30, 2019 Cash and cash equivalents $ 5.3 $ — $ — $ 5.3 U.S. stock/bond mutual funds 187.1 71.8 — 258.9 International fund 1.0 14.6 — 15.6 Total $ 193.4 $ 86.4 $ — $ 279.8 Cash and cash equivalents include money market mutual funds valued based on quoted market prices. Fair values of derivative instruments are calculated by investment managers who use valuation models that incorporate observable market inputs. Debt securities are valued based on broker/dealer quotations or by using observable market inputs. The stock and bond mutual funds are valued at the quoted market price of the identical securities. Spire Missouri The table below categorizes the fair value measurements of Spire Missouri’s pension plan assets: Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total As of September 30, 2020 Cash and cash equivalents $ 9.5 $ — $ — $ 9.5 Equity funds - global (including U.S.) 22.1 137.8 — 159.9 Equity index funds - global (including U.S.) 22.8 — — 22.8 Debt securities: U.S. bond funds 31.0 — — 31.0 U.S. government index funds 59.6 — — 59.6 Global funds (including U.S.) — 53.4 — 53.4 Total $ 145.0 $ 191.2 $ — $ 336.2 As of September 30, 2019 Cash and cash equivalents $ 41.2 $ — $ — $ 41.2 Equity mutual funds - U.S. — 9.1 — 9.1 Equity mutual funds - international — 3.3 — 3.3 Debt securities: U.S. bond mutual funds — 73.9 — 73.9 U.S. government 52.9 6.8 — 59.7 U.S. corporate 143.7 — — 143.7 U.S. municipal 4.0 — — 4.0 International 44.1 — — 44.1 Derivatives and margin receivable 0.2 — — 0.2 Total $ 286.1 $ 93.1 $ — $ 379.2 The table below categorizes the fair value measurements of Spire Missouri’s postretirement plan assets: Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total As of September 30, 2020 Cash and cash equivalents $ 3.0 $ — $ — $ 3.0 U.S. stock/bond mutual funds 196.2 — — 196.2 Total $ 199.2 $ — $ — $ 199.2 As of September 30, 2019 Cash and cash equivalents $ 5.2 $ — $ — $ 5.2 U.S. stock/bond mutual funds 183.7 — — 183.7 Total $ 188.9 $ — $ — $ 188.9 Cash and cash equivalents include money market mutual funds valued based on quoted market prices. Fair values of derivative instruments are calculated by investment managers who use valuation models that incorporate observable market inputs. Debt securities are valued based on broker/dealer quotations or by using observable market inputs. The stock and bond mutual funds are valued at the quoted market price of the identical securities. Spire Alabama The table below categorizes the fair value measurements of Spire Alabama’s pension plan assets: Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total As of September 30, 2020 Cash and cash equivalents $ 0.9 $ — $ — $ 0.9 Equity funds - global (including U.S.) 6.1 37.5 — 43.6 Equity index funds - global (including U.S.) 6.4 - — 6.4 Debt securities: U.S. bond funds 11.7 — — 11.7 U.S. government index funds 12.1 — — 12.1 Global funds (including U.S.) — 13.9 — 13.9 Total $ 37.2 $ 51.4 $ — $ 88.6 As of September 30, 2019 Cash and cash equivalents $ 0.8 $ — $ — $ 0.8 Equity mutual funds - U.S. 26.5 5.2 — 31.7 Equity mutual funds - international 19.7 3.5 — 23.2 Debt securities: U.S. bond mutual funds 22.8 — — 22.8 U.S. government — 1.7 — 1.7 International — 4.9 — 4.9 103-12 Direct Filing Entities — 8.2 — 8.2 Total $ 69.8 $ 23.5 $ — $ 93.3 The table below categorizes the fair value measurements of Spire Alabama’s postretirement plan assets: Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total As of September 30, 2020 U.S. stock/bond mutual funds $ — $ 72.2 $ — $ 72.2 International fund — 14.8 — 14.8 Total $ — $ 87.0 $ — $ 87.0 As of September 30, 2019 U.S. stock/bond mutual funds $ — $ 71.8 $ — $ 71.8 International fund — 14.6 — 14.6 Total $ — $ 86.4 $ — $ 86.4 Cash and cash equivalents include money market mutual funds valued based on quoted market prices. Fair values of derivative instruments are calculated by investment managers who use valuation models that incorporate observable market inputs. Debt securities are valued based on broker/dealer quotations or by using observable market inputs. The stock and bond mutual funds are valued at the quoted market price of the identical securities.

Information by Operating Segmen

Information by Operating Segment	12 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Information by Operating Segment	14. INFORMATION BY OPERATING SEGMENT The Company has two reportable segments: Gas Utility and Gas Marketing. The Gas Utility segment is the aggregation of the operations of the Utilities. The Gas Marketing segment includes the results of Spire Marketing, a subsidiary engaged in the non-regulated marketing of natural gas and related activities, including utilizing natural gas storage contracts for providing natural gas sales. Other components of the Company’s consolidated information include: • unallocated corporate items, including certain debt and associated interest costs; • Spire STL Pipeline, a subsidiary of Spire which has constructed and, as of November 2019, operates a 65-mile FERC-regulated pipeline to deliver natural gas into eastern Missouri; • Spire Storage, a subsidiary of Spire providing physical natural gas storage services; and • Spire’s subsidiaries engaged in the operation of a propane pipeline, the compression of natural gas, and risk management, among other activities. Accounting policies are described in Note 1 Management evaluates the performance of the operating segments based on the computation of net economic earnings. Net economic earnings exclude from reported net income the after-tax impacts of fair value accounting and timing adjustments associated with energy-related transactions, the impacts of acquisition, divestiture and restructuring activities, and the largely non-cash impacts of other non-recurring or unusual items such as certain regulatory, legislative or GAAP standard-setting actions. In fiscal 2019, this included impacts from ISRS rulings against Spire Missouri. In fiscal 201 8 , these items include d the revaluation of deferred tax assets and liabilities due to the Tax Cuts and Jobs Act and the write-off of certain long-standing assets as a result of disallowances in Spire Missouri ’s rate proceedings. 2020 Gas Utility Gas Marketing Other Eliminations Consolidated Revenues from external customers $ 1,751.8 $ 87.9 $ 15.7 $ — $ 1,855.4 Intersegment revenues 0.2 — 42.1 (42.3 ) — Total Operating Revenues 1,752.0 87.9 57.8 (42.3 ) 1,855.4 Operating Expenses Natural gas 660.2 65.1 0.4 (29.6 ) 696.1 Other operation and maintenance 421.3 11.8 38.2 (12.7 ) 458.6 Depreciation and amortization 189.7 0.6 7.0 — 197.3 Taxes, other than income taxes 146.5 1.1 0.8 — 148.4 Impairments — — 148.6 — 148.6 Total Operating Expenses 1,417.7 78.6 195.0 (42.3 ) 1,649.0 Operating Income (Loss) $ 334.3 $ 9.3 $ (137.2 ) $ — $ 206.4 Net Economic Earnings (Loss) $ 213.4 $ 9.1 $ (14.7 ) $ — $ 207.8 Capital Expenditures $ 547.8 $ 3.6 $ 87.0 $ — $ 638.4 2019 Gas Utility Gas Marketing Other Eliminations Consolidated Revenues from external customers $ 1,859.2 $ 83.7 $ 9.5 $ — $ 1,952.4 Intersegment revenues 1.6 — 12.0 (13.6 ) — Total Operating Revenues 1,860.8 83.7 21.5 (13.6 ) 1,952.4 Operating Expenses Natural gas 794.6 47.9 0.5 (2.7 ) 840.3 Other operation and maintenance 441.7 11.7 31.6 (10.9 ) 474.1 Depreciation and amortization 179.4 0.1 2.2 — 181.7 Taxes, other than income taxes 151.7 0.8 1.5 — 154.0 Total Operating Expenses 1,567.4 60.5 35.8 (13.6 ) 1,650.1 Operating Income (Loss) $ 293.4 $ 23.2 $ (14.3 ) $ — $ 302.3 Net Economic Earnings (Loss) $ 199.8 $ 19.4 $ (24.1 ) $ — $ 195.1 Capital Expenditures $ 565.4 $ 3.1 $ 254.8 $ — $ 823.3 2018 Gas Utility Gas Marketing Other Eliminations Consolidated Revenues from external customers $ 1,888.0 $ 71.6 $ 5.4 $ — $ 1,965.0 Intersegment revenues 0.4 — 11.1 (11.5 ) — Total Operating Revenues 1,888.4 71.6 16.5 (11.5 ) 1,965.0 Operating Expenses Natural gas 842.6 30.2 0.3 (1.4 ) 871.7 Other operation and maintenance 449.7 7.4 30.3 (10.1 ) 477.3 Depreciation and amortization 167.0 — 1.4 — 168.4 Taxes, other than income taxes 152.5 0.2 0.8 — 153.5 Total Operating Expenses 1,611.8 37.8 32.8 (11.5 ) 1,670.9 Operating Income (Loss) $ 276.6 $ 33.8 $ (16.3 ) $ — $ 294.1 Net Economic Earnings (Loss) $ 183.1 $ 22.9 $ (22.3 ) $ — $ 183.7 Capital Expenditures $ 457.7 $ — $ 41.7 $ — $ 499.4 Total Assets at End of Year 2020 2019 2018 Gas Utility $ 6,716.2 $ 6,094.6 $ 5,606.7 Gas Marketing 182.7 212.3 295.3 Other 2,443.5 2,692.7 2,508.0 Eliminations (1,101.2 ) (1,380.4 ) (1,566.4 ) Total Assets $ 8,241.2 $ 7,619.2 $ 6,843.6 Reconciliation of Consolidated Net Income to Consolidated Net Economic Earnings 2020 2019 2018 Net Income $ 88.6 $ 184.6 $ 214.2 Adjustments, pre-tax: Impairments 148.6 — — Provision for ISRS rulings — 12.2 — Missouri regulatory adjustments — — 30.6 Fair value and timing adjustments 2.5 1.2 (4.3 ) Acquisition, divestiture and restructuring activities — 0.4 13.6 Income tax effect of adjustments (31.9 ) (3.3 ) (10.3 ) Effect of the Tax Cuts and Jobs Act — — (60.1 ) Net Economic Earnings $ 207.8 $ 195.1 $ 183.7

Regulatory Matters

Regulatory Matters	12 Months Ended
	Sep. 30, 2020
Regulated Operations [Abstract]
Regulatory Matters	15. REGULATORY MATTERS As discussed below for Spire Missouri and Spire Alabama, the Purchased Gas Adjustment (PGA) clauses and Gas Supply Adjustment (GSA) riders allow the Utilities to pass through to customers the cost of purchased gas supplies. Regulatory assets and regulatory liabilities related to the PGA clauses and the GSA rider are both labeled Unamortized Purchased Gas Adjustments herein. The following regulatory assets and regulatory liabilities were reflected in the Balance Sheets as of September 30, 2020 and 2019. Spire Spire Missouri Spire Alabama September 30 2020 2019 2020 2019 2020 2019 Regulatory Assets: Current: Pension and postretirement benefit costs $ 30.6 $ 30.1 $ 21.9 $ 21.9 $ 7.7 $ 7.3 Unamortized purchased gas adjustments 5.5 18.2 — — 5.5 17.7 Other 33.4 30.3 10.2 7.5 7.2 8.9 Total Current Regulatory Assets 69.5 78.6 32.1 29.4 20.4 33.9 Noncurrent: Future income taxes due from customers 123.5 111.0 114.6 102.9 2.2 2.2 Pension and postretirement benefit costs 439.3 416.6 332.6 333.3 98.2 77.2 Cost of removal 395.6 150.9 7.1 — 388.6 150.9 Unamortized purchased gas adjustments 12.1 9.1 12.1 9.1 — — Energy efficiency 39.6 35.0 39.6 35.0 — — Other 59.3 45.0 42.7 27.2 0.9 0.9 Total Noncurrent Regulatory Assets 1,069.4 767.6 548.7 507.5 489.9 231.2 Total Regulatory Assets $ 1,138.9 $ 846.2 $ 580.8 $ 536.9 $ 510.3 $ 265.1 Regulatory Liabilities: Current: Pension and postretirement benefit costs $ 5.8 $ 5.8 $ 3.6 $ 3.6 $ 2.2 $ 2.2 Unamortized purchased gas adjustments 73.1 26.2 72.3 25.4 — — Other 34.1 28.8 27.3 23.3 1.7 1.2 Total Current Regulatory Liabilities 113.0 60.8 103.2 52.3 3.9 3.4 Noncurrent: Deferred taxes due to customers 138.8 179.8 121.4 162.5 — — Pension and postretirement benefit costs 157.6 142.3 140.4 119.1 14.8 19.1 Accrued cost of removal 28.6 41.6 — 15.7 — — Unamortized purchased gas adjustments 4.4 — 4.4 — — — Other 14.3 35.3 8.6 29.2 3.7 3.9 Total Noncurrent Regulatory Liabilities 343.7 399.0 274.8 326.5 18.5 23.0 Total Regulatory Liabilities $ 456.7 $ 459.8 $ 378.0 $ 378.8 $ 22.4 $ 26.4 A portion of the Company’s regulatory assets are not earning a return and are shown in the schedule below: Spire Spire Missouri September 30 2020 2019 2020 2019 Pension and postretirement benefit costs $ 232.3 $ 211.1 $ 232.3 $ 211.1 Future income taxes due from customers 121.3 108.8 114.6 102.9 Other 12.9 14.3 12.9 14.3 Total Regulatory Assets Not Earning a Return $ 366.5 $ 334.2 $ 359.8 $ 328.3 Like all the Company’s regulatory assets, these regulatory assets are expected to be recovered from customers in future rates. The recovery period for the future income taxes due from customers and pension and other postretirement benefit costs could be 20 years or longer, based on current Internal Revenue Service guidelines and average remaining service life of active participants, respectively. The other items not earning a return are expected to be recovered over a period not to exceed 15 years, consistent with precedent set by the MoPSC. Spire Alabama does not have any regulatory assets that are not earning a return. Spire Missouri As authorized by the MoPSC, the PGA clause allows Spire Missouri to flow through to customers, subject to prudence review by the MoPSC, the cost of purchased gas supplies. To better match customer billings with market natural gas prices, Spire Missouri is allowed to file to modify, on a periodic basis, the level of gas costs in its PGA. Certain provisions of the PGA clause are included below: • Spire Missouri has a risk management policy that allows for the purchase of natural gas derivative instruments with the goal of managing price risk associated with purchasing natural gas on behalf of its customers. The MoPSC clarified that costs, cost reductions, and carrying costs associated with the Utility’s use of natural gas derivative instruments are gas costs recoverable through the PGA mechanism. • The tariffs allow Spire Missouri flexibility to make up to three discretionary PGA changes during each year, in addition to its mandatory November PGA change, so long as such changes are separated by at least two months. • Spire Missouri is authorized to apply carrying costs to all over- or under-recoveries of gas costs, including costs and cost reductions associated with the use of derivative instruments, including cash payments for margin deposits. • The MoPSC approved a plan applicable to Spire Missouri’s gas supply commodity costs under which it retains a portion of cost savings associated with the acquisition of natural gas below an established benchmark level. This gas supply cost management program allows Spire Missouri to retain 10% of cost savings, up to a maximum of $3.0 annually. Spire Missouri did not record any such incentive compensation under the plan during the three fiscal years reported. Incentives recorded under the plan, if any, are included in Gas Utility Operating Revenues on the Consolidated Statements of Income and under Operating Revenues on Spire Missouri’s Statements of Comprehensive Income. Pursuant to the provisions of the PGA clause, the difference between actual costs incurred and costs recovered through the application of the PGA clause are reflected as a deferred charge or credit at the end of the fiscal year. At that time, the balance is classified as a current asset or current liability and recovered from, or credited to, customers over an annual period commencing in November. The balance in the current account is amortized as amounts are reflected in customer billings. The PGA clause also provides for the treatment of income from off-system sales and capacity release revenues. Pre-tax income from off-system sales and capacity release revenues is shared with customers, with an estimated amount assumed in PGA rates. The difference between the actual amount allocated to customers for each fiscal year and the estimated amount assumed in PGA rates is recovered from, or credited to, customers over an annual period commencing in the subsequent November. Before April 19, 2018, the customer share of such income ranged from 70% to 85%. In the latest rate cases (discussed in the following paragraphs), the multiple sharing tiers and percentages were eliminated in favor of a single sharing percentage under which customers receive 75% (and Spire Missouri receives 25%) of the net margins achieved as a result of such off-system sales and capacity releases. On March 7, 2018, the MoPSC issued its order in two general rate cases (docketed as GR-2017-0215 and GR-2017-0216), approving new tariffs that became effective on April 19, 2018. Certain provisions of the order allow less future recovery of certain deferred or capitalized costs than estimated based upon previous rate proceedings, and management determined that the related regulatory assets should be written down or off in connection with the preparation of the financial statements for the second quarter of 2018. The charges totaled $38.4 for the year ended September 30, 2018, and are included primarily in operation and maintenance expense on the statements of income and in other cash flows from operating activities on the statements of cash flows. The after-tax reduction to net income and earnings per share was $23.6 and $0.49, respectively. The charges related to the long-standing pension and real estate assets, totaling $30.6, were excluded in the determination of 2018 net economic earnings, as shown in Note 14 , Spire Missouri filed Infrastructure System Replacement Surcharge (ISRS) applications which were approved by the MoPSC and the costs associated therewith were included in new tariffs that went into effect from its last general rate cases on April 19, 2018. Since then, ISRS filings became effective on October 8, 2018, May 25, 2019, November 16, 2019, and May 25, 2020, bringing total authorized future annualized ISRS revenues for Spire Missouri to $40.3 as of September 30, 2020. An incremental $7.0 annualized ISRS rate increase was approved by the MoPSC on November 12, 2020, this increase is expected to be effective in late November or early December 2020. On November 19, 2019, the Missouri Western District Court of Appeals issued rulings (“ISRS rulings”) that determined certain capital investments in 2016 through 2018 were not eligible for recovery under the ISRS. The ISRS rulings upheld appeals by the OPC that contested recovery of portions of Spire Missouri’s ISRS and overturned the three prior MoPSC decisions. As a result of the rulings, Spire Missouri recorded a $12.2 provision for fiscal year 2019 and an additional $4.8 in the first half of fiscal year 2020. In the third quarter of fiscal 2020, Spire Missouri reached a settlement with the MoPSC staff and the OPC to resolve these cases, which was subsequently approved by the MoPSC. Pursuant to the settlement, Spire Missouri has made a customer refund in the total amount of $15.0 as a one-time bill credit issued in August 2020. The favorable difference between the total provision and the actual settlement was recorded to earnings in the third quarter. Additional ISRS appeals were taken by Spire Missouri and the OPC relating to the January 2019 ISRS filings with annual authorized revenue of $12.4, as approved by the MoPSC effective May 25, 2019, and the July 2019 ISRS filings with annual authorized revenue totaling $8.8, which was approved by the MoPSC effective November 16, 2019. The January 2019 ISRS decision has been upheld by the Western District, resulting in no revenue change or customer refund. On October 20, 2020, the Western District issued its opinion in the July 2019 case upholding the MoPSC’s decision, resulting in no revenue change or customer refund. House Bill 2120 was passed by the General Assembly on May 15, 2020, and signed into law by Missouri Governor Parson on July 2, 2020, clarifying which infrastructure investments qualify for ISRS recovery under the statute governing the ISRS mechanism. The provisions of the bill became effective August 28, 2020, and apply to new ISRS applications made on or after that date. In September 2020, Spire Missouri, the MoPSC staff and the OPC reached a Unanimous Stipulation and Agreement regarding Spire Missouri’s request for an Accounting Authority Order (AAO) pertaining to certain costs and lost customer fee revenue related to the COVID-19 pandemic. In October 2020, the MoPSC issued an order approving that agreement and granting an AAO. Accordingly, Spire Missouri recorded a regulatory asset of $3.8 as of September 30, 2020, related to the deferral of applicable costs and is tracking lost customer fee revenue. All ratemaking treatment of the deferrals and any revenue recoveries is reserved for consideration in Spire Missouri’s next general rate case. On October 8, 2020, Spire Missouri filed a Notice of Intended Rate Case Filing with the M oPSC , indicating its intention to initiate a general base rate case more than 60 days following the filing of the n otice. The n otice indicates Spire Missouri ’s intention to seek rate recovery for investments made since its last general rate case, as well as a need to reset the ISRS cap which has been reached for its western operating unit . The n otice further indicates Spire Missouri ’s intention to further unify its operating units through the anticipated tariff filings. Spire Alabama Effective January 1, 2014, Spire Alabama’s allowed range of return on average common equity (ROE) was 10.5% to 10.95% with an adjusting point of 10.8%. Spire Alabama was eligible to receive a performance-based adjustment of 5 basis points to the ROE adjusting point, based on meeting certain customer satisfaction criteria. Under its Rate Stabilization and Equalization (RSE) rate-setting process, the APSC conducts quarterly reviews to determine whether Spire Alabama’s ROE at the end of the rate year will be within the allowed range of return. Reductions in rates can be made quarterly to bring the projected ROE within the allowed range; increases, however, are allowed only once each rate year, effective December 1, and cannot exceed 4% of prior-year revenues. In October 2018, the APSC approved the renewal of RSE through September 30, 2022, with several modifications. Effective October 1, 2018, Spire Alabama’s allowed range of ROE is 10.15% to 10.65% with an adjusting point of 10.4%. Spire Alabama is eligible to receive a performance-based adjustment of +/- 10 basis point to the ROE adjusting point, based upon the terms of the newly approved Accelerated Infrastructure Modernization (AIM) Program tariff. The 5-basis point adjustment for certain customer satisfaction criteria has been removed. Other modifications include an equity limitation as a percent of total capitalization from 56.5% to 55.5% and adjustments to the Cost Control Measure (CCM) as noted below. On November 25, 2019, Spire Alabama filed an increase for rate year 2020 of $5.9, which became effective December 1, 2019. On October 26, 2020, Spire Alabama made its annual RSE rate filing with the APSC, presenting the utility’s budget for the fiscal year ending September 30, 2021, including net income and a calculation of allowed ROE. The AIM mechanism provides for a 10 basis-point increase in the allowed ROE each year if a prescribed number of pipeline miles are replaced. Spire Alabama exceeded the threshold for 2020 and accordingly filed for a 10.5% ROE for fiscal 2021. Spire Alabama’s rate schedules for natural gas distribution charges contain a GSA rider which permits the pass-through to customers of changes in the cost of gas supply. Spire Alabama’s tariff provides a temperature adjustment mechanism, also included in the GSA rider, which is designed to moderate the impact of departures from normal temperatures on Spire Alabama’s earnings. The temperature adjustment applies primarily to residential, small commercial and small industrial customers. Other non-temperature weather-related conditions that may affect customer usage are not included in the temperature adjustment. In November 2019, the APSC approved Spire Alabama’s proposal to establish a mechanism under its GSA rider allowing the utility to create value through off-system sales of excess natural gas supply and capacity and to retain 25% of the value created while giving 75% of the value to customers. The mechanism was effective with the establishment of new rates on December 1, 2019. Spire Alabama filed a GSA rate decrease effective February 1, 2020, of approximately $13.9 (on an annual basis) primarily attributable to lower natural gas prices and results of the off-system sale and capacity release share program. The inflation-based CCM, established by the APSC, allows for annual increases to operation and maintenance (“O&M”) expense. If rate year O&M expense falls within the index range, no adjustment is required. If rate year O&M expense exceeds the index range, three-quarters of the difference is returned to customers through future rate adjustments. To the extent rate year O&M is less than the index range, Spire Alabama benefits by one-half of the difference through future rate adjustments. Certain items that fluctuate based on situations demonstrated to be beyond Spire Alabama’s control may be excluded from the CCM calculation. Before fiscal 2019, the CCM index range was Spire Alabama’s 2007 actual rate year O&M expense inflation-adjusted based on the June Consumer Price Index For All Urban Consumers (CPI-U) each rate year, plus or minus 1.75%. Effective October 1, 2018, the CCM is calculated based upon O&M expense per customer and the index range is Spire Alabama’s actual 2018 O&M expense adjusted for inflation and adjusted by 2/3 and 1/3 of the 2018 CCM differential (amount below the CCM range in 2018) in 2019 and 2020, respectively, plus or minus 1.50%. As of September 30, 2020, Spire Alabama recorded an RSE point of test giveback of $3.0 and a CCM benefit of $5.2 for rate year 2020, which will both be reflected in rates effective December 1, 2020. The CCM benefit was $5.9 for rate year 2019 and $9.7 for rate year 2018. On June 28, 2010, the APSC approved a reduction in depreciation rates, effective June 1, 2010, and a regulatory liability to be recorded for Spire Alabama. Refunds from such negative salvage liability were passed back to eligible customers on a declining basis through lower tariff rates through rate year 2019 pursuant to the terms of the Negative Salvage Rebalancing (NSR) rider. The total amount refundable to customers was subject to adjustments for charges made to the Enhanced Stability Reserve (ESR) and other APSC-approved charges. The refunds were due to a re-estimation of future removal costs provided for through the prior depreciation rates. For fiscal 2019 and 2018, NSR amounts returned to customers were approximately $4.2 and $7.2, respectively. The APSC approved an ESR in 1998, which was subsequently modified and expanded in 2010. As currently approved, the ESR provides deferred treatment and recovery for the following: (1) extraordinary O&M expenses related to environmental response costs; (2) extraordinary O&M expenses related to self-insurance costs that exceed $1.0 per occurrence; (3) extraordinary O&M expenses, other than environmental response costs and self-insurance costs, resulting from a single force majeure event or multiple force majeure events greater than $0.3 and $0.4, respectively, during a rate year; and (4) negative individual large commercial and industrial customer budget revenue variances that exceed $0.4 during a rate year. Spire Alabama is tracking costs and other impacts of COVID-19 in anticipation that some of these items could be recoverable under its ESR, but no related changes to regulatory assets or liabilities have been recorded to date. Charges to the ESR are subject to certain limitations which may disallow deferred treatment and which prescribe the timing of recovery. Funding to the ESR is provided as a reduction to the refundable negative salvage balance over its nine-year nine-year five-year Spire Alabama has APSC approval for an intercompany revolving credit agreement allowing Spire Alabama to borrow from Spire in a principal amount not to exceed $200.0 at any time outstanding in combination with its bank line of credit, and to loan to Spire in a principal amount not to exceed $25.0 at any time outstanding. Borrowings may be used for the following purposes: (a) meeting increased working capital requirements; (b) financing construction requirements related to additions, extensions, and replacements of the distribution systems; and (c) financing other expenditures that may arise from time to time in the normal course of business. In fiscal 2019, the APSC approved Spire Alabama’s applications for $90.0 and $100.0 of long-term debt financing (issued January 15, 2019, and December 2, 2019, respectively). On March 24, 2020, the APSC approved an application for up to $150.0 of additional long-term debt financing for Spire Alabama. Spire In addition to those discussed above for Spire Missouri and Spire Alabama, Spire is affected by the following regulatory matters. Spire Gulf has similar rate regulation to Spire Alabama. The RSE allowed range of ROE is 10.45% to 10.95% with an adjusting point of 10.7%. The CCM has the same return and similar recovery provisions when expenses exceed or are under a band of +/- 1.50% around the CPI-U inflated O&M per customer expense level from 2017, excluding expenses for pensions and gas bad debt. Additionally, it has a Cast Iron Main Replacement factor that provides an enhanced return on the pro-rata costs associated with cast iron main replacement exceeding 10 miles per year based on a 75% weighting for the equity content. Spire Gulf also has an ESR for negative revenue variances over $0.1 or a force majeure event expense of $0.1 (or two events that exceed $0.15), a Self Insurance Reserve for general liability coverage, and an Environmental Cost Recovery Factor that recovers 90% of prudently incurred costs for compliance with environmental laws, rules and regulations. It also has an APSC-approved intercompany revolving credit agreement with Spire to borrow in a principal amount not to exceed $50.0, and to loan up to $25.0. Spire Gulf recorded a July 31, 2020, point of test refund under the RSE rate mechanism for approximately $1.4 and also recorded a CCM benefit for rate year 2020 of $1.8. On October 23, 2020, Spire Gulf made its annual RSE rate filing with the APSC based on its budget for fiscal 2021 and an allowed ROE of 10.7%, reflecting an increase in annual revenue of $1.1, pending APSC review. Spire Gulf’s rates were reduced $1.9 effective February 1, 2018, to reflect lower income taxes resulting from the TCJA. Spire Mississippi utilizes a formula rate-making process under the Rate Stabilization Adjustment (RSA) Rider. It is based on a formulaically derived return on equity (currently 9.79%), and is updated on an annual basis if the equity return on an end of period rate base is beyond the allowed return on equity by 1.0%, with 75% of any shortfall recovered through a rate increase and 50% of any excess resulting in a rate decrease. Updates may include known and measurable adjustments to historic costs from the 12 months ended June 30, submitted September 15 for an effective date of November 1, unless disputed by the Mississippi Public Utilities Staff (MPUS), with any disputes to be resolved by the MSPSC by January 15 of the following year. In December 2015, a Supplemental Growth Rider (SGR) was approved for a 3-year period to provide recovery of certain system expansion projects. On September 4, 2018, the SGR was extended to October 15, 2021. On February 5, 2019, the MSPSC approved an agreement between Spire Mississippi and the MPUS settling its Rates Stabilization and Adjustments filing that was made on September 14, 2018, resulting in a $0.7 increase in the annualized revenue requirement. New rates became effective March 1, 2019. On December 11, 2019, the MSPSC approved an agreement between Spire Mississippi and the MPUS settling its RSA filing that was made on August 30, 2019, resulting in a $0.3 increase in annual revenue. New rates became effective December 11, 2019. On August 28, 2020, Spire Mississippi filed its RSA for the rate year ended June 30, 2020, that reflected an increase to annual revenue totaling $0.6. This RSA filing is being reviewed by the MPUS. In August 2018, the Federal Energy Regulatory Commission (FERC) approved an order issuing a Certificate of Public Convenience and Necessity for the Spire STL Pipeline (“August 2018 Order”), and in November 2018, the FERC issued a Notice to Proceed, allowing construction to begin. In November 2019, Spire STL Pipeline received FERC authorization to place the STL Pipeline into service. Also, in November 2019, the FERC issued an Order on Rehearing of the August 2018 Order dismissing or denying the outstanding requests for rehearing filed by several parties, dismissing the request for stay filed by one party, and noting the withdrawal of the request for rehearing by another party. On January 21, 2020, two of the rehearing parties filed petitions for review of the FERC’s orders with the U.S. Court of Appeals for the District of Columbia Circuit. Spire STL Pipeline and Spire Missouri have intervened and filed responsive briefs in this proceeding, which remains pending. In August 2019, Spire Storage filed with the FERC two Prior Notice Applications of its intent to convert a total of six existing observation wells into injection/withdrawal wells and to install related gas flowlines, fuel gas lines and fiber optic communication. The applications cleared FERC authorization in October and November 2019, and both projects remain under development. On October 9, 2020,

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	16. COMMITMENTS AND CONTINGENCIES Commitments The Company and the Utilities have entered into contracts with various counterparties, expiring on dates through 2032, for the storage, transportation, and supply of natural gas. Minimum payments required under the contracts in place at September 30, 2020, are estimated at $1,745.4, $1,410.3 and $229.7 for the Company, Spire Missouri and Spire Alabama, respectively. Additional contracts are generally entered into prior to or during the heating season of November through April. The Utilities recover their costs from customers in accordance with their PGA clauses or GSA riders. Spire NGL Inc. is providing liquid propane transportation service to Spire Missouri pursuant to an approved FERC tariff and a contractual arrangement with Spire Missouri. In accordance with the terms of that agreement, Spire Missouri is obligated to pay Spire NGL Inc. approximately $1.0 annually, at current rates. The agreement will terminate March 31, 2021. A consolidated subsidiary is a general partner in an unconsolidated partnership that invests in real estate partnerships. The subsidiary and third parties are jointly and severally liable for the payment of mortgage loans in the aggregate outstanding amount of approximately $1.2 incurred in connection with various real estate ventures. Spire has no reason to believe that the other principal liable parties will not be able to meet their proportionate share of these obligations. Spire further believes that the asset values of the real estate properties are sufficient to support these mortgage loans. Contingencies The Company and the Utilities account for contingencies, including environmental liabilities, in accordance with accounting standards under the loss contingency guidance of ASC Topic 450, Contingencies In addition to matters noted below, the Company and the Utilities are involved in other litigation, claims, and investigations arising in the normal course of business. Management, after discussion with counsel, believes the final outcome will not have a material effect on the statements of income, balance sheets, and statements of cash flows of the Company, Spire Missouri, or Spire Alabama. However, there is uncertainty in the valuation of pending claims and prediction of litigation results. The Company and the Utilities own and operate natural gas distribution, transmission, and storage facilities, the operations of which are subject to various environmental laws, regulations, and interpretations. While environmental issues resulting from such operations arise in the ordinary course of business, such issues have not materially affected the Company’s or Utilities’ financial position and results of operations. As environmental laws, regulations, and their interpretations change, the Company or the Utilities may incur additional environmental liabilities that may result in additional costs, which may be material. In the natural gas industry, many gas distribution companies have incurred environmental liabilities associated with sites they or their predecessor companies formerly owned or operated where manufactured gas operations took place. The Utilities each have former manufactured gas plant (MGP) operations in their respective service territories. To the extent costs are incurred associated with environmental remediation activities, the Utilities would request authority from their respective regulators to defer such costs (less any amounts received from insurance proceeds or as contributions from other potentially responsible parties (PRPs)) and collect them through future rates. Spire Missouri Spire Missouri has identified three former MGP sites in the city of St. Louis, Missouri (the “City”) where costs have been incurred and claims have been asserted. Spire Missouri has enrolled two of the sites in the Missouri Department of Natural Resources (MDNR) Brownfields/Voluntary Cleanup Program (BVCP). The third site is the result of a relatively new claim assertion by the United States Environmental Protection Agency (EPA). In conjunction with redevelopment of one of the sites, Spire Missouri and another former owner of the site entered into an agreement (the “Remediation Agreement”) with the City development agencies, the developer, and an environmental consultant that obligates one of the City agencies and the environmental consultant to remediate the site and obtain a No Further Action letter from the MDNR. The Remediation Agreement also provides for a release of Spire Missouri and the other former site owner from certain liabilities related to the past and current environmental condition of the site and requires the developer and the environmental consultant to maintain certain insurance coverage, including remediation cost containment, premises pollution liability, and professional liability. The operative provisions of the Remediation Agreement were triggered on December 20, 2010, on which date Spire Missouri and the other former site owner, as full consideration under the Remediation Agreement, paid a small percentage of the cost of remediation of the site. Spire Missouri has not owned the second site for many years. In a letter dated June 29, 2011, the Attorney General for the State of Missouri informed Spire Missouri that the MDNR had completed an investigation of the site. The Attorney General requested that Spire Missouri participate in the follow up investigations of the site. In a letter dated January 10, 2012, Spire Missouri stated that it would participate in future environmental response activities at the site in conjunction with other PRPs that are willing to contribute to such efforts in a meaningful and equitable fashion. Accordingly, Spire Missouri entered into a cost sharing agreement for remedial investigation with other PRPs. To date, MDNR has not approved the agreement, so remedial investigation has not yet occurred. Additionally, in correspondence dated November 30, 2016, Region 7 of the EPA has asserted that Spire Missouri is liable under Section 107(a) of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) for alleged coal gas waste contamination at a third site in the northern portion of the City on which Spire Missouri operated a MGP. Spire Missouri has not owned or operated the site (also known as Station “B”) for over 70 years. Spire Missouri and the site owner have met with the EPA and reviewed its assertions. Both Spire Missouri and the site owner have notified the EPA that information and data provided by the EPA to date does not rise to the level of documenting a threat to the public health or environment. As such, Spire Missouri requested more information from the EPA, some of which would also be utilized to identify other former owners and operators of the site that could be added as PRPs. To date, Spire Missouri has not received a response from the EPA. Spire Missouri has notified its insurers that it seeks reimbursement for costs incurred in the past and future potential liabilities associated with these MGP sites. While some of the insurers have denied coverage and reserved their rights, Spire Missouri retains the right to seek potential reimbursements from them. On March 10, 2015, Spire Missouri received a Section 104(e) information request under CERCLA from EPA Region 7 regarding the former Thompson Chemical/Superior Solvents site in the City. In turn, Spire Missouri issued a Freedom of Information Act (FOIA) request to the EPA on April 3, 2015, in an effort to identify the basis of the inquiry. The FOIA response from the EPA was received on July 15, 2015, and a response was provided to the EPA on August 15, 2015. Spire Missouri has received no further inquiry from the EPA regarding this matter. In its western service area, Spire Missouri has seven owned MGP sites enrolled in the BVCP, including Joplin MGP #1, St. Joseph MGP #1, Kansas City Coal Gas Station B, Kansas City Station A Railroad area, Kansas City Coal Gas Station A North, Kansas City Coal Gas Station A South, and Independence MGP #2. Source removal has been conducted at all of the owned sites since 2003 with the exception of Joplin. On September 15, 2016, a request was made with the MDNR for a restrictive covenant use limitation with respect to Joplin. Remediation efforts at the seven sites are at various stages of completion, ranging from groundwater monitoring and sampling following source removal activities to the aforementioned request in respect to Joplin. As part of its participation in the BVCP, Spire Missouri communicates regularly with the MDNR with respect to its remediation efforts and monitoring activities at these sites. On May 11, 2015, MDNR approved the next phase of investigation at the Kansas City Station A North and Railroad areas. To date, costs incurred for all Spire Missouri ’s MGP sites for investigation, remediation and monitoring these sites have not been material. However, the amount of costs relative to future remedial actions at these and other sites is unknown and may be material. The actual future costs that Spire Missouri may incur could be materially higher or lower depending upon several factors, including whether remediation will be required, final selection and regulatory approval of any remedial actions, changing technologies and government regulations, the ultimate ability of other PRPs to pay, and any insurance recoveries. In 2013, Spire Missouri retained an outside consultant to conduct probabilistic cost modeling of 19 former MGP sites owned or operated by Spire Missouri. The purpose of this analysis was to develop an estimated range of probabilistic future liability for each site. That analysis, completed in August 2014, provided a range of demonstrated possible future expenditures to investigate, monitor and remediate all 19 MGP sites. Spire Missouri has recorded its best estimate of the probable expenditures that relate to these matters. The amount is not material. Spire Missouri and the Company do not expect potential liabilities that may arise from remediating these sites to have a material impact on their future financial condition or results of operations. Spire Alabama Spire Alabama is in the chain of title of nine former MGP sites, four of which it still owns, and five former manufactured gas distribution sites, one of which it still owns. Spire Alabama does not foresee a probable or reasonably estimable loss associated with these sites. Spire Alabama and the Company do not expect potential liabilities that may arise from remediating these sites to have a material impact on their future financial condition or results of operations. In 2012, Spire Alabama responded to an EPA Request for Information Pursuant to Section 104 of CERCLA relating to the 35th Avenue Superfund Site located in North Birmingham, Jefferson County, Alabama. Spire Alabama was identified as a PRP under CERCLA for the cleanup of the site or costs the EPA incurs in cleaning up the site. At this point, Spire Alabama has not been provided information that would allow it to determine the extent, if any, of its potential liability with respect to the 35th Avenue Superfund Site and vigorously denies its inclusion as a PRP. Spire In addition to those discussed above for Spire Missouri and Spire Alabama, Spire is aware of the following contingent matter. In February 2018, the Company was made aware of a complaint filed with the U.S. Department of Housing and Urban Development (HUD) by the South Alabama Center for Fair Housing and the National Community Reinvestment Coalition. The complaint alleges that Spire Gulf discriminated against unspecified residents of Eight Mile, Alabama, on the basis of race in violation of the Fair Housing Act by failing to adequately address the odorant release that occurred in 2008. The Company believes there is no basis for the complaint, HUD has no jurisdiction in the matter, and there will be no material impact on its future financial condition or results of operations.

Leases

Leases	12 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Leases	17. LEASES The lease agreement covering the Company’s primary office space in St. Louis extends through February 2035, with an option to renew for an additional five years. Spire Alabama’s lease agreement for office space in Birmingham extends through January 2024. The lease agreement covering Spire Marketing and Spire Storage office space in Houston extends through December 2028, with options to terminate three years earlier or to renew for an additional five years. The renewal options in the St. Louis and Houston leases are reasonably certain to be exercised and are included in the lease term used to determine the right-of use assets and lease liabilities. The Company and its subsidiaries have other relatively minor rental arrangements for real estate and equipment with remaining terms of up to ten years. Operating lease cost, cash flow and noncash information for the year ended September 30, 2020, are shown in the following table. Spire Spire Missouri Spire Alabama Operating lease cost, including amounts capitalized $ 8.7 $ 0.5 $ 3.5 Cash flow and noncash information about operating leases: Operating cash flows representing cash paid for amounts included in the measurement of lease liabilities 8.5 0.5 3.3 Right-of-use assets obtained in exchange for lease liabilities 71.1 2.1 10.0 The following table shows balance sheet and weighted-average information about operating leases as of September 30, 2020. Balance sheet classification Spire Spire Missouri Spire Alabama Right-of-use assets Deferred Charges and Other Assets: Other $ 65.1 $ 1.7 $ 6.7 Lease liabilities, current Current Liabilities, Other 6.5 0.3 1.9 Lease liabilities, noncurrent Deferred Credits and Other Liabilities: Other 58.4 1.4 4.7 Weighted-average remaining lease term 15.9 years 5.3 years 3.3 years Weighted-average discount rate 4.2 % 2.5 % 2.2 % Following is a maturity analysis by fiscal year for operating lease liabilities as of September 30, 2020. Spire Spire Missouri Spire Alabama 2021 $ 6.6 $ 0.3 $ 1.9 2022 7.2 0.4 2.1 2023 7.2 0.3 2.1 2024 5.8 0.3 0.7 2025 5.1 0.3 — Thereafter 58.4 0.2 — Total undiscounted lease payments 90.3 1.8 6.8 Less present value discount (25.4 ) (0.1 ) (0.2 ) Total current and noncurrent lease liabilities $ 64.9 $ 1.7 $ 6.6 The aggregate rental expense for fiscal years 2018 and 2019 and the annual minimum rental commitments for all leases having an initial or remaining non-cancelable term of more than one year as of September 30, 2019, were as follows (under ASC 840). Aggregate Rental Expense Minimum Rental Commitments as of September 30, 2019 2018 2019 2020 2021 2022 2023 2024 Later Total Spire $ 10.0 $ 10.9 $ 8.2 $ 7.0 $ 6.8 $ 6.1 $ 4.8 $ 36.5 $ 69.4 Spire Missouri 3.6 3.7 0.5 0.2 — — — — 0.7 Spire Alabama 4.7 5.2 2.9 2.1 2.1 2.1 0.7 — 9.9 There are no significant finance leases, short-term leases, subleases, variable lease payments, residual value guarantees, restrictions or covenants pertaining to leases. The Company elected, for all asset classes, not to recognize right-of-use assets and lease liabilities for short-term leases. Instead, the lease payments are recognized in profit or loss on a straight-line basis over the lease term and variable lease payments are recognized in the period in which the obligation for those payments is incurred. The Company elected, for all asset classes, not to separate nonlease components from lease components and instead to account for each separate lease component and the nonlease components associated with that lease component as a single lease component. The discount rate used for all the leases is the applicable incremental borrowing rate, which is the rate of interest that a lessee would have to pay to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. For a subsidiary lessee, the rate applicable to the subsidiary is used unless the lease terms are influenced by parent credit.

Interim Financial Information (

Interim Financial Information (Unaudited)	12 Months Ended
	Sep. 30, 2020
Quarterly Financial Information Disclosure [Abstract]
Interim Financial Information (Unaudited)	18. INTERIM FINANCIAL INFORMATION (UNAUDITED) Spire In the opinion of Spire, the quarterly information presented below for fiscal years 2020 and 2019 includes all adjustments necessary for a fair statement of the results of operations for such periods. Variations in consolidated operations reported on a quarterly basis primarily reflect the seasonal nature of the business of the Utilities. Three Months Ended Dec. 31 March 31 June 30 Sept. 30 Fiscal Year 2020 Total Operating Revenues $ 566.9 $ 715.5 $ 321.1 $ 251.9 Operating Income (Loss) 102.3 210.5 (106.5 ) 0.1 Net Income (Loss) 67.0 133.6 (92.3 ) (19.7 ) Basic Earnings (Loss) Per Share of Common Stock $ 1.24 $ 2.55 $ (1.87 ) $ (0.45 ) Diluted Earnings (Loss) Per Share of Common Stock $ 1.24 $ 2.54 $ (1.87 ) $ (0.45 ) Fiscal Year 2019 Total Operating Revenues $ 602.0 $ 803.5 $ 321.3 $ 225.6 Operating Income (Loss) 105.1 209.5 13.3 (25.6 ) Net Income (Loss) 67.3 154.6 (3.0 ) (34.3 ) Basic Earnings (Loss) Per Share of Common Stock $ 1.33 $ 3.05 $ (0.09 ) $ (0.75 ) Diluted Earnings (Loss) Per Share of Common Stock $ 1.32 $ 3.04 $ (0.09 ) $ (0.74 ) Spire Missouri In the opinion of Spire Missouri, the quarterly information presented below for fiscal years 2020 and 2019 includes all adjustments necessary for a fair statement of the results of operations for such periods. Variations in operations reported on a quarterly basis primarily reflect their seasonal nature. Three Months Ended Dec. 31 March 31 June 30 Sept. 30 Fiscal Year 2020 Total Operating Revenues $ 374.0 $ 457.5 $ 203.9 $ 158.2 Operating Income 67.0 117.7 7.0 13.9 Net Income 48.0 74.5 6.5 1.2 Fiscal Year 2019 Total Operating Revenues $ 413.2 $ 556.6 $ 191.4 $ 130.6 Operating Income (Loss) 71.4 102.4 12.2 (11.2 ) Net Income (Loss) 51.2 80.0 1.1 (17.3 ) Spire Alabama In the opinion of Spire Alabama, the quarterly information presented below for fiscal years 2020 and 2019 includes all adjustments necessary for a fair statement of the results of operations for such periods. Variations in operations reported on a quarterly basis primarily reflect their seasonal nature. Three Months Ended Dec. 31 March 31 June 30 Sept. 30 Fiscal Year 2020 Total Operating Revenues $ 126.2 $ 185.5 $ 81.2 $ 62.1 Operating Income (Loss) 20.9 81.2 9.3 (8.5 ) Net Income (Loss) 13.2 57.8 3.6 (8.9 ) Fiscal Year 2019 Total Operating Revenues $ 133.5 $ 180.4 $ 90.8 $ 60.8 Operating Income (Loss) 17.1 79.6 11.1 (12.3 ) Net Income (Loss) 10.3 56.7 5.6 (12.3 )

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	BASIS OF PRESENTATION – These notes are an integral part of the accompanying audited financial statements of Spire Inc. (“Spire” or the “Company”) presented on a consolidated basis, Spire Missouri Inc. (“Spire Missouri”) and Spire Alabama Inc. (“Spire Alabama”). Spire Missouri and Spire Alabama are wholly owned subsidiaries of Spire. Spire Missouri, Spire Alabama and the subsidiaries of Spire EnergySouth Inc. (“Spire EnergySouth”) are collectively referred to as the “Utilities.” The subsidiaries of Spire EnergySouth are Spire Gulf Inc. and Spire Mississippi Inc. Unless otherwise indicated, references to years herein are references to the fiscal years ending September 30 for the Company and its subsidiaries. The accompanying audited financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP). The consolidated financial position, results of operations and cash flows of Spire include the accounts of the Company and all its subsidiaries. Transactions and balances between consolidated entities have been eliminated from the consolidated financial statements of Spire. In compliance with GAAP, transactions between Spire Missouri and Spire Alabama and their affiliates, as well as intercompany balances on their balance sheets, have not been eliminated from their separate financial statements.
Use of Estimates	USE OF ESTIMATES – The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates.
System of Accounts	SYSTEM OF ACCOUNTS – The accounts of the Utilities are maintained in accordance with the Uniform System of Accounts prescribed by the applicable state public service commissions, which systems substantially conform to that prescribed by the Federal Energy Regulatory Commission (FERC).
Property, Plant, and Equipment	PROPERTY, PLANT, AND EQUIPMENT – Utility Plant – Utility plant is stated at original cost. The cost of additions to utility plant includes contracted work, direct labor and materials, allocable overheads and an allowance for funds used during construction. The costs of units of property retired, replaced or renewed are removed from utility plant and are charged to accumulated depreciation. Maintenance and repairs of property and replacement and renewal of items determined to be less than units of property are charged to maintenance expenses. For Spire Missouri, utility plant is depreciated on a straight-line basis at rates based on estimated service lives of the various classes of property. In fiscal year 2020, the average depreciation and amortization expense averaged 2.9%, while in fiscal years 2019 and 2018, annual depreciation and amortization expense averaged 3.0% of the original cost of depreciable and amortizable property. For Spire Alabama, depreciation is provided using the composite method of depreciation on a straight-line basis over the estimated useful lives of utility property at rates approved by the Alabama Public Service Commission (APSC). The composite depreciation rate in fiscal years 2020, 2019 and 2018 was approximately 3.1%. Non-utility Property – Non-utility property is recorded at the original cost of acquisition or construction, which includes material, labor, contractor services and, for FERC-regulated projects, an allowance for funds used during construction. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Upon retirement or sale of non-utility property, the original cost and related accumulated depreciation are removed from the accounts and any gain or loss is included in the income statements. Costs related to software developed or obtained for internal use are capitalized and amortized on a straight-line basis over the estimated useful life of the related software. If software is retired prior to being fully amortized, the difference is recorded as a loss in the income statements.
Accrued Capital Expenditures	Accrued Capital Expenditures – Accrued capital expenditures, shown in the following table, are excluded from capital expenditures in the statements of cash flows until paid. September 30 2020 2019 2018 Spire $ 67.6 $ 80.6 $ 62.1 Spire Missouri 34.3 40.1 36.7 Spire Alabama 17.0 11.9 8.9
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS – Spire, Spire Missouri and Spire Alabama record legal obligations associated with the retirement of long-lived assets in the period in which the obligations are incurred, if sufficient information exists to reasonably estimate the fair value of the obligations. Obligations are recorded as both a cost of the related long-lived asset and as a corresponding liability. Subsequently, the asset retirement costs are depreciated over the life of the asset and the asset retirement obligations are accreted to the expected settlement amounts. The Company, Spire Missouri and Spire Alabama record asset retirement obligations associated with certain safety requirements to purge and seal gas distribution mains upon retirement, the plugging and abandonment of storage wells and other storage facilities, specific service line obligations, and certain removal and disposal obligations related to components of Spire Missouri’s, Spire Alabama’s and Spire Gulf’s distribution systems and general plant. Asset retirement obligations recorded by Spire’s other subsidiaries are not material. As authorized by the Missouri Public Service Commission (MoPSC) and APSC, Spire Missouri, Spire Alabama and Spire Gulf accrue future asset removal costs associated with their property, plant and equipment even if a legal obligation does not exist. Such accruals are provided for through depreciation expense and are recorded with corresponding credits to regulatory liabilities or regulatory assets. When those utilities retire depreciable utility plant and equipment, they charge the associated original costs to accumulated depreciation and amortization, and any related removal costs incurred are charged to regulatory liabilities or regulatory assets. The difference between removal costs recognized in depreciation rates and the accretion expense and depreciation expense recognized for financial reporting purposes is a timing difference between recovery of these costs in rates and their recognition for financial reporting purposes. Accordingly, these differences are deferred as regulatory liabilities or regulatory assets. In the rate setting process, the regulatory liabilities or regulatory assets are excluded from the rate base upon which those utilities have the opportunity to earn their allowed rates of return. In fiscal 2020, Spire Alabama refined certain assumptions and estimates used in calculating its asset retirement obligations, resulting in both an increase in cost to retire gas distribution assets and a change in the timing of the related cash outflows. As a result of this change in estimate, which the Company believes is more precise, Spire Alabama recorded a $221.1 increase to its asset retirement obligations. Related adjustments were made to regulatory assets and utility plant, with no impact on earnings. The following table presents a reconciliation of the beginning and ending balances of asset retirement obligations at September 30, as reported in the balance sheets. Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Asset retirement obligations, beginning of year $ 337.6 $ 321.1 $ 173.5 $ 174.1 $ 148.7 $ 135.7 Liabilities incurred during the period 3.0 10.8 2.6 1.6 — 8.8 Liabilities settled during the period (6.9 ) (8.3 ) (4.0 ) (6.8 ) (1.6 ) (0.8 ) Accretion 14.0 13.0 7.2 7.4 6.1 5.0 Revisions in estimated cash flows 192.4 1.0 (25.9 ) (2.8 ) 221.1 — Asset retirement obligations, end of year $ 540.1 $ 337.6 $ 153.4 $ 173.5 $ 374.3 $ 148.7
Regulated Operations	REGULATED OPERATIONS – The Utilities account for their regulated operations in accordance with Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC) Topic 980, Regulated Operations . This topic sets forth the application of GAAP for those companies whose rates are established by or are subject to approval by an independent third-party regulator. The provisions of this accounting guidance require, among other things, that financial statements of a regulated enterprise reflect the actions of regulators, where appropriate. These actions may result in the recognition of revenues and expenses in time periods that are different than non-regulated enterprises. When this occurs, costs are deferred as assets in the balance sheet (regulatory assets) and recorded as expenses when those amounts are reflected in rates. In addition, regulators can impose liabilities upon a regulated company for amounts previously collected from customers and for recovery of costs that are expected to be incurred in the future (regulatory liabilities). Management believes that the current regulatory environment supports the continued use of these regulatory accounting principles and that all regulatory assets and regulatory liabilities are recoverable or refundable through the regulatory process. See additional discussion on regulated operations in Note 15 , Regulatory Matters.
Natural Gas and Propane Gas	NATURAL GAS AND PROPANE GAS – For Spire Missouri’s eastern region, inventory of natural gas in storage is priced on a last in, first out (LIFO) basis and inventory of propane gas in storage is priced on a first in, first out (FIFO) basis. For the rest of the Gas Utility segment, inventory of natural gas in storage is priced on the weighted average cost basis. The replacement cost of Spire Missouri’s natural gas for current use in eastern Missouri at September 30, 2020, and September 30, 2019, was less than the LIFO cost by $12.5 and $17.0, respectively. The carrying value of the Utilities’ inventory is never adjusted to a lower net realizable value or market value because, pursuant to Purchased Gas Adjustment (PGA) clauses or a Gas Supply Adjustment (GSA) rider, actual gas costs are recovered in customer rates. Natural gas and propane gas storage inventory in Spire’s other operating segments is recorded at the lower of average cost or net realizable value.
Business Combinations	BUSINESS COMBINATIONS – Spire’s acquisitions were accounted for using business combination accounting. Under this method, the purchase price paid by the acquirer is allocated to the assets acquired and liabilities assumed as of the acquisition date based on their fair value. In December 2017, the Company acquired an 80% voting interest in a natural gas storage facility in Wyoming. The transaction was valued at $24.8, consisting of $16.0 in cash and a $10.0 non-interest-bearing note valued at $8.8. In October 2018, the Company completed the exercise of its right to call the remaining 20% voting interest in that facility and settled the related note for a combined total of $17.0. In May 2018, the Company expanded its operations by acquiring 100% of a neighboring natural gas storage facility for $12.2 in cash. Together, these storage operations are referred to herein as “Spire Storage.”
Goodwill	GOODWILL – Goodwill is measured as the excess of the acquisition-date fair value of the consideration transferred over the amount of acquisition-date identifiable assets acquired net of assumed liabilities. At September 30, 2020, goodwill included in Spire’s Gas Utility and Gas Marketing segments was $210.2 and zero, respectively, with the remainder held at the corporate level. Goodwill amounts have not changed since fiscal 2017, and there are no accumulated impairment losses. Spire and Spire Missouri evaluate goodwill for impairment as of July 1 of each year, or more frequently if events and circumstances indicate that goodwill might be impaired. At July 1, 2020 and 2019, Spire and Spire Missouri conducted qualitative assessments and determined goodwill was not impaired. The Company updated the assessments as of September 30, 2020, determining that it remained more likely than not that the fair value of each reporting unit exceeded its carrying value.
Impairment of Long-lived Assets	IMPAIRMENT OF LONG-LIVED ASSETS – Long-lived assets classified as held and used are evaluated for impairment when events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. Whether impairment has occurred is determined by comparing the estimated undiscounted cash flows attributable to the assets with the carrying value of the assets. If the carrying value exceeds the undiscounted cash flows, the Company recognizes an impairment charge equal to the amount of the carrying value that exceeds the estimated fair value of the assets. In the period in which the Company determines an asset meets held-for-sale criteria, an impairment charge is recorded to the extent the book value exceeds its fair value less cost to sell. On July 1, 2020, Spire’s Board of Directors, based upon the recommendation of senior management, revised the development plan for Spire Storage, resulting in an impairment charge of $140.8 related to Spire Storage assets (non-utility property on the balance sheet) in the quarter ended June 30, 2020. The revision was driven by the realization that a longer time horizon will be required for optimization and positioning of the storage facility to serve energy markets in the western United States. Among other factors, evaluations of the continuing evolution of market dynamics in the region led management to update models of various development alternatives. Separately in the quarter ended June 30, 2020, Spire recorded impairment charges totaling $7.8 related to two commercial compressed natural gas fueling stations (also non-utility property) as a result of revised projections reflecting lower diesel prices and slower conversions of Class 8 vehicles. The fair values used in measuring the impairment charges were determined with an expected present value technique using a discounted cash flow method under an income approach.
Derivatives	DERIVATIVES – In the course of their business, certain subsidiaries of Spire enter into commitments associated with the purchase or sale of natural gas. Certain of their derivative natural gas contracts are designated as normal purchases or normal sales and, as such, are excluded from the scope of FASB ASC Topic 815, Derivatives and Hedging . Those contracts are accounted for as executory contracts and recorded on an accrual basis. Revenues and expenses from such contracts are recorded gross. Contracts not designated as normal purchases or normal sales are recorded as derivatives with changes in fair value recognized in earnings in the periods prior to physical delivery. Certain of Spire Marketing’s wholesale purchase and sale transactions are classified as trading activities for financial reporting purposes. Under GAAP, revenues and expenses associated with trading activities are presented on a net basis in Gas Marketing operating revenues (or expenses, if negative) in the Condensed Consolidated Statements of Income. This net presentation has no effect on operating income or net income. Refer to Note 10 , Derivative Instruments and Hedging Activities, for more information about derivatives.
Income Taxes	INCOME TAXES – Spire and its subsidiaries account for income taxes under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amount of existing assets and liabilities and the respective tax basis and for tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be realized or settled. The effects on deferred tax assets and liabilities of a change in enacted tax rates is recognized in income or loss for non-regulated operations, and in a regulatory asset or regulatory liability for regulated operations. A valuation allowance is established when it is more likely than not that some portion or all of the deferred tax assets will not be realized. The Company accounts for uncertain tax positions in accordance with authoritative guidance. The authoritative guidance addresses the determination of whether tax benefits claimed, or expected to be claimed, on a tax return should be recorded in the financial statements. Spire may recognize the tax benefit from an uncertain tax position only if it is more likely than not that the position will be sustained upon examination by the taxing authority, based on the technical merits of the position. Tax-related interest and penalties, if any, are classified as a liability on the balance sheets. For additional information on the accounting for income taxes, refer to Note 12 , Income Taxes.
Cash, Cash Equivalents, and Restricted Cash	CASH, CASH EQUIVALENTS, AND RESTRICTED CASH – All highly liquid debt instruments purchased with original maturities of three months or less are considered to be cash equivalents. Such instruments are carried at cost, which approximates market value. Outstanding checks on the Company’s and Utilities’ bank accounts in excess of funds on deposit create book overdrafts (which are funded at the time checks are presented for payment) and are classified as Other in the Current Liabilities section of the balance sheets. Changes in book overdrafts are reflected as Operating Activities in the statements of cash flows. In Spire’s statements of cash flows, total cash, cash equivalents, and restricted cash included $17.0 of restricted cash reported in “Other” current assets on Spire’s balance sheet as of September 30, 2018 (in addition to amounts shown as “Cash and cash equivalents”). This restricted cash was an escrow deposit for the purchase of the remaining 20% interest in a natural gas storage business and the settlement of the related note payable, and the transaction was completed on October 25, 2018.
Natural Gas Receivable	NATURAL GAS RECEIVABLE – Spire Marketing enters into natural gas transactions with natural gas pipeline and storage companies known as park and loan arrangements. Under the terms of the arrangements, Spire Marketing purchases natural gas from a third party and delivers that natural gas to the pipeline or storage company for the right to receive the same quantity of natural gas from that company at the same location in a future period. These arrangements are accounted for as non-monetary transactions under GAAP and are recorded at the carrying amount. As such, natural gas receivables are reflected on the Consolidated Balance Sheets at cost, which includes related fees associated with the transactions. In the period that the natural gas is returned to Spire Marketing, concurrent with the sale of the natural gas to a third party, the related natural gas receivable is expensed in the Consolidated Statements of Income. In conjunction with these transactions, Spire Marketing usually enters into New York Mercantile Exchange (NYMEX) and Intercontinental Exchange (ICE) natural gas futures, options, and swap contracts or fixed price sales agreements to protect against market changes in future sales prices. ACCOUNTS RECEIVABLE AND ALLOWANCE FOR DOUBTFUL ACCOUNTS – Trade accounts receivable are recorded at the amounts due from customers, including unbilled amounts. Estimates of the collectability of trade accounts receivable are based on historical trends, age of receivables, economic conditions, credit risk of specific customers, and other factors. Accounts receivable are written off against the allowance for doubtful accounts when they are deemed to be uncollectible. Spire Spire Missouri Spire Alabama 2020 2019 2018 2020 2019 2018 2020 2019 2018 Allowance at beginning of year $ 23.0 $ 22.4 $ 18.3 $ 14.9 $ 16.0 $ 14.1 $ 6.3 $ 3.9 $ 2.6 Additions charged to expense 14.0 16.9 14.6 12.7 12.3 11.9 0.9 4.7 2.1 Net deductions (12.1 ) (16.3 ) (10.5 ) (9.5 ) (13.4 ) (10.0 ) (1.7 ) (2.3 ) (0.8 ) Allowance at end of year $ 24.9 $ 23.0 $ 22.4 $ 18.1 $ 14.9 $ 16.0 $ 5.5 $ 6.3 $ 3.9
Earnings per Common Share	EARNINGS PER COMMON SHARE – GAAP requires dual presentation of basic and diluted earnings per share (EPS). EPS is computed using the two-class method, which is an earnings allocation method for computing EPS that treats a participating security as having rights to earnings that would otherwise have been available to common shareholders. Certain of the Company’s stock-based compensation awards pay non-forfeitable dividends to the participants during the vesting period and, as such, are deemed participating securities. Basic EPS is computed by dividing net income available to common shareholders by the weighted average number of common shares outstanding during the period. Diluted EPS is computed by dividing net income available to common shareholders by the weighted average number of common shares outstanding that are increased for additional shares that would be outstanding if potentially dilutive non-participating securities were converted to common shares, pursuant to the treasury stock method. Shares attributable to equity units, non-participating stock options and time-vested restricted stock/units are excluded from the calculation of diluted earnings per share if the effect would be antidilutive. Shares attributable to non-participating performance-contingent restricted stock awards are only included in the calculation of diluted earnings per share to the extent the underlying performance and/or market conditions are satisfied (a) prior to the end of the reporting period or (b) would be satisfied if the end of the reporting period were the end of the related contingency period and the result would be dilutive. The Company’s EPS computations are presented in Note 4 , Earnings Per Common Share.
Transactions with Affiliates	TRANSACTIONS WITH AFFILIATES – Transactions between affiliates of the Company have been eliminated from the consolidated financial statements of Spire. Spire Missouri and Spire Alabama borrowed funds from the Company and incurred related interest, as reflected in their separate financial statements, and they participated in normal intercompany shared services transactions. In addition, Spire Missouri’s other transactions with affiliates included: 2020 2019 2018 Purchases of natural gas from Spire Marketing $ 56.9 $ 95.3 $ 71.5 Sales of natural gas to Spire Marketing 0.1 1.7 0.3 Transportation services received from STL Pipeline LLC 27.9 — — Transportation services received from Spire NGL Inc. 1.0 1.0 1.0 In the twelve months ended September 30, 2020, Spire Alabama had natural gas purchases from and sales to Spire Marketing totaling $6.3 and $0.3, respectively.
Finance Receivables	FINANCE RECEIVABLES – Spire Alabama finances third party contractor sales of merchandise including gas furnaces and appliances. At September 30, 2020 and September 30, 2019, Spire Alabama’s finance receivable totaled approximately $9.4 and $11.7, respectively. Financing is available only to qualified customers who meet creditworthiness thresholds for customer payment history and external agency credit reports. Spire Alabama relies upon ongoing payments as the primary indicator of credit quality during the term of each contract. The allowance for credit losses is recognized using an estimate of write-off percentages based on historical experience. Delinquent accounts are evaluated on a case-by-case basis and, absent evidence of debt repayment, after 90 days are due in full and assigned to a third-party collection agency. The remaining finance receivable is written off approximately 12 months after being assigned to the third-party collection agency. Spire Alabama had finance receivables past due 90 days or more of $0.3 at September 30, 2020 and $0.4 at September 30, 2019.
Group Medical and Workers' Compensation Reserves	GROUP MEDICAL AND WORKERS’ COMPENSATION RESERVES – The Company self-insures its group medical and workers’ compensation costs and carries stop-loss coverage in relation to medical claims and workers’ compensation claims. Reserves for amounts incurred but not reported are established based on historical cost levels and lags between occurrences and reporting.
Fair Value Measurements	FAIR VALUE MEASUREMENTS – Certain assets and liabilities are recognized or disclosed at fair value, which is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). GAAP establishes a fair value hierarchy that prioritizes the inputs used to measure fair value. The levels of the hierarchy are described below: • Level 1 – Unadjusted quoted prices in active markets for identical assets or liabilities. • Level 2 – Pricing inputs other than quoted prices included within Level 1, which are either directly or indirectly observable for the asset or liability as of the reporting date. These inputs are derived principally from, or corroborated by, observable market data. • Level 3 – Pricing that is based upon inputs that are generally unobservable that are based on the best information available and reflect management’s assumptions about how market participants would price the asset or liability. Assessment of the significance of a particular input to the fair value measurements may require judgment and may affect the valuation of the asset or liability and its placement within the fair value hierarchy. Additional information about fair value measurements is provided in Note 8 , Fair Value of Financial Instruments, Note 9 , Fair Value Measurements, and Note 13 , Pension Plans and Other Postretirement Benefits.
Stock-based Compensation	STOCK-BASED COMPENSATION – The Company accounts for share-based compensation arrangements in accordance with ASC Topic 718, Compensation - Stock Compensation . The Company measures stock-based compensation awards at fair value at the date of grant and recognizes the compensation cost of the awards over the requisite service period. Forfeitures are recognized in the period they occur. Refer to Note 3 , Stock-Based Compensation, for further discussion of the accounting for the Company’s stock-based compensation plans.
New Accounting Pronouncements	NEW ACCOUNTING PRONOUNCEMENTS – Spire, Spire Missouri and Spire Alabama adopted the guidance in ASU No. 2014-09, Revenue from Contracts with Customers , and related amendments (collectively, “ASC 606”), in the first quarter of fiscal year 2019 using the modified retrospective method applied to all contracts at October 1, 2018. The core principle of ASC 606 is that revenue should be recognized to depict the transfer of control of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Under the new standard, an entity must identify the performance obligations in a contract, determine the transaction price and allocate the price to specific performance obligations to recognize revenue when the obligation is completed. In addition, ASC 606 requires disclosure of the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. The adoption of ASC 606 resulted in no change to how Spire, Spire Missouri and Spire Alabama recognize revenue, and therefore, no cumulative effect adjustment to the opening balance of retained earnings was required, and there was no significant impact to financial results after adoption. The adoption did result in changes to the disclosures about revenue, which are included in Note 2 , Revenue. Some revenue arrangements, such as alternative revenue programs and certain derivative contracts, are excluded from the scope of ASC 606 and, therefore, are presented separately in disclosures. Also effective October 1, 2018, Spire, Spire Missouri and Spire Alabama adopted ASU No. Compensation – Retirement Benefits : Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost The amended guidance that the of net periodic pension and postretirement benefit costs presented within line item in the income statement as other compensation costs (except for the amount being capitalized), while other components presented outside the subtotal of operating income and . The amended guidance is applied retrospectively for income statement presentation and prospectively for capitalization. The Company, Spire practical expedient permitting the use of the amounts disclosed in its pension and other postretirement benefit plan note for the prior comparative periods as the estimation basis for applying the retrospective presentation requirements. Accordingly, for the year ended September 30, 2018, the Company, Spire Missouri and Spire Alabama reclassified net benefit costs (income) of $14.4, $17.2 and $(2.0), respectively, from “operation and maintenance” to “other income (expense), net.” For Spire Missouri, Spire Alabama, and the Company’s other rate-regulated entities, all components of net benefit cost have historically been recovered from customers as a component of utility plant and will continue to be recovered in the same manner over the depreciable lives of the related plant assets; therefore, for those entities, the components that are no longer eligible to be capitalized as a component of plant under GAAP are reported as regulatory assets In February 201 8 , the FASB issued ASU 201 8 -02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income . This guidance permits companies to make an election to reclassify stranded income tax effects from the enact ment of the Tax Cuts and Jobs Act of 2017, included in accumulated other comprehensive income or loss (AOCI) , to retained earnings. The Company, Spire Missouri and Spire Alabama adopt ed this guidance in the quarter ended September 30, 201 8 , and the related reclassifications are shown on the statements of shareholders’ equity of the Company and Spire Missouri. There was no effect for Spire Alabama. The Company, Spire Missouri and Spire Alabama adopted ASU No. 2016-02, Leases Note 17 , Leases. Spire, Spire Missouri and Spire Alabama adopted the guidance in ASU No. 2017-12, Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses: Measurement of Credit Losses on Financial Instruments
Reclassifications	RECLASSIFICATIONS – Spire’s consolidated statements of income historically showed Gas Utility operating revenues and expense line items separately from Gas Marketing and other operations. The current presentation shows operating revenues and expense line items on a consolidated basis. Disaggregated data is presented in Note 14 , Information by Operating Segment. Prior period amounts have been reclassified to conform with the current period presentation.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Schedule of Capital Expenditures Excluded from Statement of Cash Flow	Accrued capital expenditures, shown in the following table, are excluded from capital expenditures in the statements of cash flows until paid. September 30 2020 2019 2018 Spire $ 67.6 $ 80.6 $ 62.1 Spire Missouri 34.3 40.1 36.7 Spire Alabama 17.0 11.9 8.9
Asset Retirement Obligations	In fiscal 2020, Spire Alabama refined certain assumptions and estimates used in calculating its asset retirement obligations, resulting in both an increase in cost to retire gas distribution assets and a change in the timing of the related cash outflows. As a result of this change in estimate, which the Company believes is more precise, Spire Alabama recorded a $221.1 increase to its asset retirement obligations. Related adjustments were made to regulatory assets and utility plant, with no impact on earnings. The following table presents a reconciliation of the beginning and ending balances of asset retirement obligations at September 30, as reported in the balance sheets. Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Asset retirement obligations, beginning of year $ 337.6 $ 321.1 $ 173.5 $ 174.1 $ 148.7 $ 135.7 Liabilities incurred during the period 3.0 10.8 2.6 1.6 — 8.8 Liabilities settled during the period (6.9 ) (8.3 ) (4.0 ) (6.8 ) (1.6 ) (0.8 ) Accretion 14.0 13.0 7.2 7.4 6.1 5.0 Revisions in estimated cash flows 192.4 1.0 (25.9 ) (2.8 ) 221.1 — Asset retirement obligations, end of year $ 540.1 $ 337.6 $ 153.4 $ 173.5 $ 374.3 $ 148.7
Schedule of Inter-Company Transactions	In addition, Spire Missouri’s other transactions with affiliates included: 2020 2019 2018 Purchases of natural gas from Spire Marketing $ 56.9 $ 95.3 $ 71.5 Sales of natural gas to Spire Marketing 0.1 1.7 0.3 Transportation services received from STL Pipeline LLC 27.9 — — Transportation services received from Spire NGL Inc. 1.0 1.0 1.0
Schedule of Allowance for Doubtful Accounts	Spire Spire Missouri Spire Alabama 2020 2019 2018 2020 2019 2018 2020 2019 2018 Allowance at beginning of year $ 23.0 $ 22.4 $ 18.3 $ 14.9 $ 16.0 $ 14.1 $ 6.3 $ 3.9 $ 2.6 Additions charged to expense 14.0 16.9 14.6 12.7 12.3 11.9 0.9 4.7 2.1 Net deductions (12.1 ) (16.3 ) (10.5 ) (9.5 ) (13.4 ) (10.0 ) (1.7 ) (2.3 ) (0.8 ) Allowance at end of year $ 24.9 $ 23.0 $ 22.4 $ 18.1 $ 14.9 $ 16.0 $ 5.5 $ 6.3 $ 3.9

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Sep. 30, 2020
Revenue From Contract With Customer [Abstract]
Schedule of Revenue Disaggregated by Source and Customer Type	The following tables show revenue disaggregated by source and customer type. 2020 2019 Spire Gas Utility: Residential $ 1,184.3 $ 1,267.3 Commercial & industrial 383.0 433.9 Transportation 115.8 112.1 Off-system & other incentive 38.4 41.9 Other customer revenue 26.2 22.5 Total revenue from contracts with customers 1,747.7 1,877.7 Changes in accrued revenue under alternative revenue programs 4.3 (16.9 ) Total Gas Utility operating revenues 1,752.0 1,860.8 Gas Marketing: Revenue from contracts with retail customers 87.9 83.7 Revenue from wholesale derivative contracts — — Total Gas Marketing operating revenues 87.9 83.7 Other 57.8 21.5 Total before eliminations 1,897.7 1,966.0 Intersegment eliminations (see Note 14, Information by Operating Segment) (42.3 ) (13.6 ) Total Operating Revenues $ 1,855.4 $ 1,952.4 Spire Missouri Residential $ 859.6 $ 945.9 Commercial & industrial 241.4 283.8 Transportation 32.9 33.1 Off-system & other incentive 35.1 41.9 Other customer revenue 22.3 — Total revenue from contracts with customers 1,191.3 1,304.7 Changes in accrued revenue under alternative revenue programs 2.3 (12.9 ) Total Operating Revenues $ 1,193.6 $ 1,291.8 Spire Alabama Residential $ 267.8 $ 265.3 Commercial & industrial 109.4 113.5 Transportation 72.9 69.5 Off-system & other incentive 3.2 — Other customer revenue 1.9 20.7 Total revenue from contracts with customers 455.2 469.0 Changes in accrued revenue under alternative revenue programs (0.2 ) (3.5 ) Total Operating Revenues $ 455.0 $ 465.5
Schedule of Gross Receipts Taxes	The expense amounts (shown in the table below) are reported gross in the “Taxes, other than income taxes” line in the statements of income, and corresponding revenues are reported in “Operating Revenues.” 2020 2019 2018 Spire $ 91.5 $ 99.3 $ 98.4 Spire Missouri 63.5 71.1 68.9 Spire Alabama 23.3 23.7 25.4

Stock-based Compensation (Table

Stock-based Compensation (Tables)	12 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Restricted Stock and Restricted Stock Unit Activity	Fiscal 2020 activity of restricted stock units subject to performance and/or market conditions is presented below: Units Weighted Average Grant Date Fair Value Per Unit Nonvested at September 30, 2019 263,910 $ 73.20 Granted 91,662 $ 76.19 Vested (86,287 ) $ 58.68 Forfeited (9,341 ) $ 79.34 Nonvested at September 30, 2020 259,944 $ 78.92 Time-vested restricted stock and stock unit activity for fiscal 2020 is presented below: Shares/ Units Weighted Average Grant Date Fair Value Per Share Nonvested at September 30, 2019 96,277 $ 72.83 Granted 33,350 $ 76.13 Vested (32,326 ) $ 65.28 Forfeited (3,628 ) $ 76.94 Nonvested at September 30, 2020 93,673 $ 76.45
Significant Assumptions Used in the Monte Carlo simulations	The significant assumptions used in the Monte Carlo simulations are as follows: 2020 2019 2018 Risk-free interest rate 1.57% 2.88% 1.76% Expected dividend yield of stock — — — Expected volatility of stock 16.8% 17.0% 16.0% Vesting period 3.0 years 3.0 years 2.9 years
Compensation Cost Recognized for Share-based Compensation Arrangements	The amounts of compensation cost recognized for share-based compensation arrangements are presented below: 2020 2019 2018 Total compensation cost $ 9.4 $ 8.6 $ 6.9 Compensation cost capitalized (0.6 ) (1.4 ) (1.3 ) Prior period disallowed stock compensation capitalization — — 6.9 Compensation cost recognized in net income 8.8 7.2 12.5 Income tax benefit recognized in net income (2.1 ) (1.7 ) (4.0 ) Compensation cost recognized in net income, net of income tax $ 6.7 $ 5.5 $ 8.5

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	12 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Earnings Per Share	2020 2019 2018 Basic Earnings Per Common Share: Net Income $ 88.6 $ 184.6 $ 214.2 Less: Provision for preferred dividends 14.8 5.3 — Income allocated to participating securities 0.1 0.4 0.5 Net Income Available to Common Shareholders $ 73.7 $ 178.9 $ 213.7 Weighted Average Common Shares Outstanding (in millions) 51.2 50.7 49.1 Basic Earnings Per Share of Common Stock $ 1.44 $ 3.53 $ 4.35 Diluted Earnings per Common Share: Net Income $ 88.6 $ 184.6 $ 214.2 Less: Provision for preferred dividends 14.8 5.3 — Income allocated to participating securities 0.1 0.4 0.5 Net Income Available to Common Shareholders $ 73.7 $ 178.9 $ 213.7 Weighted Average Common Shares Outstanding (in millions) 51.2 50.7 49.1 Dilutive Effect of Restricted Stock and Restricted Stock Units (in millions)* 0.1 0.1 0.2 Weighted Average Diluted Common Shares (in millions) 51.3 50.8 49.3 Diluted Earnings Per Share of Common Stock $ 1.44 $ 3.52 $ 4.33 * Calculation excludes certain outstanding common shares (shown in millions by period at the right) attributable to stock units subject to performance or market conditions and restricted stock, which could have a dilutive effect in the future 0.1 0.1 0.4

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	12 Months Ended
	Sep. 30, 2020
Stockholders Equity Note [Abstract]
Schedule of Accumulated Other Comprehensive Income	The components of accumulated other comprehensive income (AOCI), net of income taxes, recognized in the balance sheets at September 30 were as follows: Net Unrealized Gains (Losses) on Cash Flow Hedges Defined Benefit Pension and Other Postretirement Benefit Plans Net Unrealized Losses on Available-for- Sale Debt Securities Total Spire Balance at September 30, 2018 $ 7.9 $ (1.5 ) $ — $ 6.4 Other comprehensive (loss) income (36.9 ) (0.9 ) 0.1 (37.7 ) Balance at September 30, 2019 (29.0 ) (2.4 ) 0.1 (31.3 ) Other comprehensive loss (9.4 ) (0.5 ) — (9.9 ) Balance at September 30, 2020 $ (38.4 ) $ (2.9 ) $ 0.1 $ (41.2 ) Spire Missouri Balance at September 30, 2018 $ — $ (1.6 ) $ — $ (1.6 ) Other comprehensive loss — (0.8 ) — (0.8 ) Balance at September 30, 2019 — (2.4 ) — (2.4 ) Other comprehensive loss — (0.5 ) — (0.5 ) Balance at September 30, 2020 $ — $ (2.9 ) $ — $ (2.9 )

Long-term Debt (Tables)

Long-term Debt (Tables)	12 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Schedule of Composition of Long-term Debt	The composition of long-term debt as of September 30 is shown in the following tables. 2020 2019 Spire 2.52% Senior Notes, due September 1, 2021 $ 35.0 $ 35.0 3.31% Notes Payable, due December 15, 2022 25.0 25.0 3.54% Senior Notes, due February 27, 2024 150.0 150.0 3.13% Senior Notes, due September 1, 2026 130.0 130.0 3.93% Senior Notes, due March 15, 2027 100.0 100.0 4.70% Senior Notes, due August 15, 2044 250.0 250.0 Total principal of Spire Missouri long-term debt (see below) 1,098.0 930.0 Total principal of Spire Alabama long-term debt (see below) 475.0 415.0 Other subsidiaries' long-term debt: 4.14% First Mortgage Bonds, due September 30, 2021 20.0 20.0 5.00% First Mortgage Bonds, due September 30, 2031 42.0 42.0 2.95% Notes, with annual principal payments through December 2034 135.0 — 3.52% First Mortgage Bonds, due September 30, 2049 40.0 40.0 Total principal of long-term debt 2,500.0 2,137.0 Less: Unamortized discounts and debt issuance costs (15.9 ) (14.4 ) Less: Current portion (60.4 ) (40.0 ) Long-term debt, excluding current portion $ 2,423.7 $ 2,082.6 Spire Missouri Floating-rate note due December 1, 2021 $ — $ 100.0 First Mortgage Bonds: 3.00% Series, due March 15, 2023 55.0 55.0 3.40% Series, due August 15, 2023 250.0 250.0 3.40% Series, due March 15, 2028 45.0 45.0 7.00% Series, due June 1, 2029 19.3 25.0 2.84% Series, due November 15, 2029 275.0 — 7.90% Series, due September 15, 2030 30.0 30.0 3.68% Series, due September 15, 2032 50.0 50.0 6.00% Series, due May 1, 2034 99.3 100.0 6.15% Series, due June 1, 2036 54.5 55.0 4.63% Series, due August 15, 2043 99.9 100.0 4.23% Series, due September 15, 2047 70.0 70.0 4.38% Series, due September 15, 2057 50.0 50.0 Total principal of Spire Missouri long-term debt 1,098.0 930.0 Less: Unamortized discounts and debt issuance costs (6.0 ) (5.0 ) Less: Current portion — — Spire Missouri long-term debt, excluding current portion $ 1,092.0 $ 925.0 Spire Alabama 5.20% Notes, due January 15, 2020 $ — $ 40.0 3.86% Notes, due December 22, 2021 50.0 50.0 3.21% Notes, due September 15, 2025 35.0 35.0 2.88% Notes, due December 1, 2029 100.0 — 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 475.0 415.0 Less: Unamortized discounts and debt issuance costs (3.2 ) (2.8 ) Less: Current portion — (40.0 ) Spire Alabama long-term debt, excluding current portion $ 471.8 $ 372.2
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, 2020 are as follows: 2021 2022 2023 2024 2025 Spire $ 60.4 $ 55.8 $ 336.2 $ 156.6 $ 42.0 Spire Missouri — — 305.0 — — Spire Alabama — 50.0 — — 35.0

Notes Payable and Credit Agre_2

Notes Payable and Credit Agreements (Tables)	12 Months Ended
	Sep. 30, 2020
Short Term Borrowings [Abstract]
Schedule of Spire Missouri and Alabama Short-term Borrowings	Information about Spire’s consolidated short-term borrowings and about Spire Missouri’s and Spire Alabama’s borrowings from Spire is presented in the following table. As of September 30, 2020, $449.8 of Spire’s short-term borrowings were used to support lending to the Utilities. Spire (Parent Only) Spire Missouri Spire Alabama Spire Credit Term CP Credit Spire Credit Spire Consol- Facility Loan Program Facility Note Facility Note idated Year Ended September 30, 2020 Weighted average borrowings $ 0.1 $ 77.5 $ 476.1 $ 17.9 $ 242.0 $ 4.6 $ 89.0 $ 576.2 Lowest borrowings outstanding — — 73.5 — 16.0 — 18.5 432.6 Highest borrowings outstanding 23.1 150.0 856.6 185.1 429.5 50.0 161.3 856.6 Weighted average interest rate 1.9 % 1.6 % 1.7 % 1.9 % 1.5 % 1.9 % 1.4 % 1.7 % As of September 30, 2020 Borrowings outstanding $ — $ 150.0 $ 498.0 $ — $ 301.2 $ — $ 121.3 $ 648.0 Weighted average interest rate n/a 1.1 % 0.2 % n/a 0.2 % n/a 0.2 % 0.6 % As of September 30, 2019 Borrowings outstanding $ — $ — $ 743.2 $ — $ 386.4 $ — $ 128.7 $ 743.2 Weighted average interest rate n/a n/a 2.3 % n/a 2.3 % n/a 2.3 % 2.3 %

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Summary of Financial Instruments Measured at Fair Value on Recurring Basis	The carrying amounts and estimated fair values of financial instruments not measured at fair value on a recurring basis were as follows: Classification of Estimated Fair Value Carrying Amount Fair Value Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Spire As of September 30, 2020 Cash and cash equivalents $ 4.1 $ 4.1 $ 4.1 $ — Notes payable 648.0 648.0 — 648.0 Long-term debt, including current portion 2,484.1 2,908.6 — 2,908.6 As of September 30, 2019 Cash and cash equivalents $ 5.8 $ 5.8 $ 5.8 $ — Notes payable 743.2 743.2 — 743.2 Long-term debt, including current portion 2,122.6 2,373.4 — 2,373.4 Spire Missouri As of September 30, 2020 Notes payable - associated companies $ 301.2 $ 301.2 $ — $ 301.2 Long-term debt 1,092.0 1,313.5 — 1,313.5 As of September 30, 2019 Cash and cash equivalents $ 2.6 $ 2.6 $ 2.6 $ — Notes payable - associated companies 386.4 386.4 — 386.4 Long-term debt 925.0 1,065.2 — 1,065.2 Spire Alabama As of September 30, 2020 Notes payable - associated companies $ 121.3 $ 121.3 $ — $ 121.3 Long-term debt, including current portion 471.8 576.9 — 576.9 As of September 30, 2019 Notes payable - associated companies $ 128.7 $ 128.7 $ — $ 128.7 Long-term debt, including current portion 412.2 474.8 — 474.8

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Sep. 30, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis	Spire Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Effects of Netting and Cash Margin Receivables /Payables Total As of September 30, 2020 ASSETS Gas Utility: U.S. stock/bond mutual funds $ 21.9 $ — $ — $ — $ 21.9 Gasoline and heating oil contracts 0.3 — — (0.3 ) — NYMEX/ICE natural gas contracts 6.3 — — (6.3 ) — Gas Marketing: NYMEX/ICE natural gas contracts — 27.7 — (25.4 ) 2.3 Natural gas commodity contracts — 14.5 0.4 — 14.9 Other: U.S. stock/bond mutual funds 18.6 — — — 18.6 Total $ 47.1 $ 42.2 $ 0.4 $ (32.0 ) $ 57.7 LIABILITIES Gas Utility: NYMEX/ICE natural gas contracts $ 0.9 $ — $ — $ (0.9 ) $ — Gas Marketing: NYMEX/ICE natural gas contracts 0.7 21.4 — (22.1 ) — Natural gas commodity contracts — 22.3 — — 22.3 Other: Interest rate swaps — 54.2 — — 54.2 Total $ 1.6 $ 97.9 $ — $ (23.0 ) $ 76.5 As of September 30, 2019 ASSETS Gas Utility: U.S. stock/bond mutual funds $ 20.5 $ — $ — $ — $ 20.5 Gas Marketing: NYMEX/ICE natural gas contracts 0.9 6.5 — (6.9 ) 0.5 Natural gas commodity contracts — 16.8 — (2.5 ) 14.3 Other: U.S. stock/bond mutual funds 15.5 — — — 15.5 Total $ 36.9 $ 23.3 $ — $ (9.4 ) $ 50.8 LIABILITIES Gas Utility: NYMEX/ICE natural gas contracts $ 12.3 $ — $ — $ (12.3 ) $ — Gas Marketing: NYMEX/ICE natural gas contracts 0.4 8.5 — (8.9 ) — Natural gas commodity contracts — 13.8 0.1 (2.5 ) 11.4 Other: Interest rate swaps — 43.4 — — 43.4 Total $ 12.7 $ 65.7 $ 0.1 $ (23.7 ) $ 54.8
Spire Missouri
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis	Spire Missouri Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Effects of Netting and Cash Margin Receivables /Payables Total As of September 30, 2020 ASSETS U.S. stock/bond mutual funds $ 21.9 $ — $ — $ — $ 21.9 Gasoline and heating oil contracts 0.3 — — (0.3 ) — NYMEX/ICE natural gas contracts 6.3 — — (6.3 ) — Total $ 28.5 $ — $ — $ (6.6 ) $ 21.9 LIABILITIES NYMEX/ICE natural gas contracts $ 0.9 $ — $ — $ (0.9 ) $ — As of September 30, 2019 ASSETS U.S. stock/bond mutual funds $ 20.5 $ — $ — $ — $ 20.5 LIABILITIES NYMEX/ICE natural gas contracts $ 12.3 $ — $ — $ (12.3 ) $ —

Derivative Instruments and He_2

Derivative Instruments and Hedging Activities (Tables)	12 Months Ended
	Sep. 30, 2020
Derivative [Line Items]
Derivative Instruments and Hedging Activities	Open NYMEX and ICE natural gas futures and swap positions at September 30, 2020 and 2019 were as follows: September 30, 2020 September 30, 2019 Gas Marketing Notional (MMBtu millions) Maximum Term (Months) Notional (MMBtu millions) Maximum Term (Months) Natural gas futures purchased 22.9 41 29.1 36 Natural gas options purchased, net 4.8 6 6.9 12 Natural gas basis swaps purchased 6.2 24 90.1 36 Gas Utility Natural gas futures purchased 25.9 12 69.0 12
Effect of Derivative Instruments on Statements of Consolidated Income and Statements of Consolidated Comprehensive Income	Effect of Derivative Instruments on the Consolidated Statements of Income and Comprehensive Income Location of Gain (Loss) Recorded in Income 2020 2019 2018 Derivatives in Cash Flow Hedging Relationships Effective portion of gain (loss) recognized in OCI on derivatives: Interest rate swaps (8.9 ) (46.4 ) 3.9 Total $ (8.9 ) $ (46.4 ) $ 3.9 Effective portion of gain (loss) reclassified from AOCI to income: Gasoline and heating oil contracts Gas Utility Other Operating Expenses — — 0.1 Interest rate swaps Interest Expense (3.2 ) 1.3 1.4 Total $ (3.2 ) $ 1.3 $ 1.5 Derivatives Not Designated as Hedging Instruments* Gain (loss) recognized in income on derivatives: Natural gas commodity contracts Gas Marketing Operating Revenues $ 9.2 $ 2.5 $ 10.2 Gas Marketing Operating Expenses — (8.4 ) (8.1 ) NYMEX / ICE natural gas contracts Gas Marketing Operating Revenues (11.8 ) — — Total $ (2.6 ) $ (5.9 ) $ 2.1 * Gains and losses on Spire Missouri’s natural gas derivative instruments, which are not designated as hedging instruments for financial reporting purposes, are deferred pursuant to the Missouri Utilities’ PGA clauses and initially recorded as regulatory assets or regulatory liabilities. These gains and losses are excluded from the table above because they have no direct impact on the statements of income. Such amounts are recognized in the statements of income as a component of Regulated Gas Distribution Natural and Propane Gas operating expenses when they are recovered through the PGA clause and reflected in customer billings.
Fair Value of Derivative Instruments in the Consolidated Balance Sheet	Fair Value of Derivative Instruments in the Consolidated Balance Sheets Derivative Assets* Derivative Liabilities* September 30, 2020 Balance Sheet Location Fair Value Balance Sheet Location Fair Value Derivatives designated as hedging instruments Other: Interest rate swaps Derivative Instrument Liability $ — Derivative Instrument Liability $ 54.2 Subtotal — 54.2 Derivatives not designated as hedging instruments Gas Utility: Natural gas contracts Accounts Receivable – Other 6.3 Accounts Receivable – Other 0.9 Gasoline and heating oil contracts Derivative Instrument Assets 0.3 — Gas Marketing: NYMEX / ICE natural gas contracts Derivative Instrument Assets 20.5 Derivative Instrument Assets 21.3 Deferred Charges – Other 7.2 Deferred Charges – Other 0.8 Natural gas commodity Derivative Instrument Assets 13.5 Derivative Instrument Assets — Deferred Charges – Other 1.4 Deferred Charges – Other — Current Liabilities – Other — Current Liabilities – Other 16.8 Deferred Credits – Other — Deferred Credits – Other 5.5 Subtotal 49.2 45.3 Total derivatives $ 49.2 $ 99.5 September 30, 2019 Derivatives designated as hedging instruments Other: Interest rate swaps Derivative Instrument Liability $ — Derivative Instrument Liability $ 43.4 Subtotal — 43.4 Derivatives not designated as hedging instruments Gas Utility: Natural gas contracts Accounts Receivable – Other — Accounts Receivable – Other 12.3 Gas Marketing: NYMEX / ICE natural gas contracts Derivative Instrument Assets 7.0 Derivative Instrument Assets 7.3 Deferred Charges – Other 0.5 Deferred Charges – Other 1.6 Natural gas commodity Derivative Instrument Assets 10.4 Derivative Instrument Assets 0.9 Deferred Charges – Other 4.8 Deferred Charges – Other — Current Liabilities – Other 1.4 Current Liabilities – Other 11.5 Deferred Credits – Other 0.1 Deferred Credits – Other 1.5 Subtotal 24.2 35.1 Total derivatives $ 24.2 $ 78.5 * The fair values of Derivative Assets and Derivative Liabilities exclude the fair value of cash margin receivables or payables with counterparties subject to netting arrangements. Fair value amounts of derivative contracts (including the fair value amounts of cash margin receivables and payables) for which there is a legal right to set off are presented net on the balance sheets. As such, the gross balances presented in the table above are not indicative of the Company’s net economic exposure. Refer to Note 9
Derivative Instruments Reconciliation	Following is a reconciliation of the amounts in the tables above to the amounts presented in the Consolidated Balance Sheets: 2020 2019 Fair value of derivative assets presented above $ 49.2 $ 24.2 Fair value of cash margin receivable offset with derivatives (9.0 ) 14.3 Netting of assets and liabilities with the same counterparty (23.0 ) (23.7 ) Total $ 17.2 $ 14.8 Derivative Instrument Assets, per Consolidated Balance Sheets: Current Assets – Other $ 15.8 $ 4.2 Deferred Charges and Other Assets – Other 1.4 10.6 Total $ 17.2 $ 14.8 Fair value of derivative liabilities presented above $ 99.5 $ 78.5 Netting of assets and liabilities with the same counterparty (23.0 ) (23.7 ) Total $ 76.5 $ 54.8 Derivative Instrument Liabilities, per Consolidated Balance Sheets: Current Liabilities – Other $ 71.0 $ 50.0 Deferred Credits and Other Liabilities – Other 5.5 4.8 Total $ 76.5 $ 54.8
Spire Missouri
Derivative [Line Items]
Derivative Instruments and Hedging Activities	Spire Missouri’s derivative instruments consist primarily of NYMEX positions. The NYMEX is the primary national commodities exchange on which natural gas derivatives are traded. Open NYMEX natural gas futures positions at September 30, 2020 were as follows: September 30, 2020 Notional (MMBtu millions) Maximum Term (Months) Natural gas futures purchased 25.9 12
Effect of Derivative Instruments on Statements of Consolidated Income and Statements of Consolidated Comprehensive Income	Effect of Derivative Instruments on the Statements of Comprehensive Income Location of Gain (Loss) Recorded in Income 2020 2019 2018 Derivatives in Cash Flow Hedging Relationships Effective portion of gain (loss) recognized in OCI on derivatives: Gasoline and heating oil contracts $ — $ — $ — Effective portion of gain (loss) reclassified from AOCI to income: Gasoline and heating oil contracts Gas Utility Other Operating Expenses $ — $ — $ 0.1 * Gains and losses on Spire Missouri’s natural gas derivative instruments, which are not designated as hedging instruments for financial reporting purposes, are deferred pursuant to the Spire Missouri’s PGA clauses and initially recorded as regulatory assets or regulatory liabilities. These gains and losses are excluded from the table above because they have no direct impact on the Statements of Income. Such amounts are recognized in the Statements of Income as a component of Regulated Gas Distribution Natural and Propane Gas operating expenses when they are recovered through the PGA clause and reflected in customer billings.
Fair Value of Derivative Instruments in the Consolidated Balance Sheet	Fair Value of Derivative Instruments in the Balance Sheets Derivative Assets* Derivative Liabilities* September 30, 2020 Balance Sheet Location Fair Value Balance Sheet Location Fair Value Derivatives not designated as hedging instruments Natural gas contracts Accounts Receivable – Other $ 6.3 Accounts Receivable – Other $ 0.9 Gasoline and heating oil contracts Derivative Instrument Assets 0.3 — Total derivatives $ 6.6 $ 0.9 September 30, 2019 Derivatives not designated as hedging instruments Natural gas contracts Accounts Receivable – Other $ — Accounts Receivable – Other $ 12.3 * The fair values of Derivative Assets and Derivative Liabilities exclude the fair value of cash margin receivables or payables with counterparties subject to netting arrangements. Fair value amounts of derivative contracts (including the fair value amounts of cash margin receivables and payables) for which there is a legal right to set off are presented net on the Balance Sheets. As such, the gross balances presented in the table above are not indicative of Spire Missouri’s net economic exposure. Refer to Note 9
Derivative Instruments Reconciliation	Following is a reconciliation of the amounts in the tables above to the amounts presented in Spire Missouri’s Balance Sheets: 2020 2019 Fair value of derivative assets presented above $ 6.6 $ — Fair value of cash margin (payable) receivable offset with derivatives (5.7 ) 12.3 Netting of assets and liabilities with the same counterparty (0.9 ) (12.3 ) Total $ — $ — Fair value of derivative liabilities presented above $ 0.9 $ 12.3 Netting of assets and liabilities with the same counterparty (0.9 ) (12.3 ) Total $ — $ —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Net Provision for Income Tax	The provision (benefit) for income taxes during the fiscal years ended September 30, 2020, 2019, and 2018 was as follows: Spire Spire Missouri Spire Alabama 2020 2019 2018 2020 2019 2018 2020 2019 2018 Federal: Current $ 0.4 $ 0.6 $ — $ — $ — $ — $ — $ — $ — Deferred 5.8 27.4 (22.7 ) 14.9 11.5 (26.1 ) 17.4 16.3 81.5 Investment tax credits (0.2 ) (0.2 ) (0.2 ) (0.2 ) (0.2 ) (0.2 ) — — — State and local: Current 3.0 2.1 2.2 0.1 — — — — — Deferred 3.4 4.6 (5.8 ) 2.5 2.0 (6.3 ) 4.6 4.2 0.1 Total income tax expense (benefit) $ 12.4 $ 34.5 $ (26.5 ) $ 17.3 $ 13.3 $ (32.6 ) $ 22.0 $ 20.5 $ 81.6
Effective Income Tax Rate Variation from Stated Tax Rate	The effective income tax rate varied from the federal statutory income tax rate for each year due to the following: Spire Spire Missouri Spire Alabama 2020 2019 2018 2020 2019 2018 2020 2019 2018 Federal income tax statutory rate 21.0 % 21.0 % 24.5 % 21.0 % 21.0 % 24.5 % 21.0 % 21.0 % 24.5 % State and local income taxes, net of federal income tax benefits 9.0 3.6 3.4 2.6 2.6 3.4 4.1 4.1 3.8 Certain expenses capitalized on books and deducted on tax return (6.6 ) (3.8 ) (2.3 ) (4.6 ) (6.5 ) (4.6 ) — — — Taxes related to prior years (1.8 ) 0.2 (0.4 ) (1.4 ) 0.1 (0.7 ) 0.1 — — Tax law changes — — (35.9 ) — — (50.3 ) — — 70.0 Amortization of excess deferred taxes (8.3 ) (3.8 ) (1.8 ) (5.7 ) (6.6 ) (3.6 ) — — — Other items – net * (1.0 ) (1.4 ) (1.6 ) (0.2 ) (0.3 ) (2.5 ) (0.1 ) 0.2 0.1 Effective income tax rate 12.3 % 15.8 % (14.1 )% 11.7 % 10.3 % (33.8 )% 25.1 % 25.3 % 98.4 % * Other consists primarily of property adjustments.
Significant Items in Net Deferred Tax Liability	The significant items comprising the net deferred tax liability or asset as of September 30 were as follows: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Deferred tax assets: Reserves not currently deductible $ 24.8 $ 31.4 $ 16.7 $ 21.2 $ 5.9 $ 6.2 Pension and other postretirement benefits 108.3 102.7 78.5 78.7 — — Goodwill — — — — 101.3 116.8 Operating losses 170.4 162.2 36.0 51.1 111.3 94.2 Regulatory amount due to customers, net 36.1 46.5 32.3 42.7 — — Other 44.7 20.0 — 1.2 — — Deferred tax assets 384.3 362.8 163.5 194.9 218.5 217.2 Less: Valuation allowance (0.9 ) (1.8 ) (0.9 ) (1.8 ) — — Total deferred tax assets 383.4 361.0 162.6 193.1 218.5 217.2 Deferred tax liabilities: Relating to property (614.0 ) (562.9 ) (427.1 ) (395.1 ) (151.4 ) (129.3 ) Regulatory pension and other postretirement benefits (138.4 ) (135.9 ) (107.4 ) (111.7 ) (3.4 ) (2.0 ) Other** (142.4 ) (113.6 ) (62.8 ) (50.9 ) (4.4 ) (4.6 ) Total deferred tax liabilities (894.8 ) (812.4 ) (597.3 ) (557.7 ) (159.2 ) (135.9 ) Net deferred tax (liability) asset $ (511.4 ) $ (451.4 ) $ (434.7 ) $ (364.6 ) $ 59.3 $ 81.3 ** For Spire, Other consists primarily of goodwill-related liabilities. Spire Spire Missouri Spire Alabama Adjustment to deferred tax liabilities $ (318.3 ) $ (285.3 ) $ (61.0 ) Adjustment to deferred income tax expense (75.0 ) (57.0 ) 58.8 Adjustment to regulatory assets (75.9 ) (78.1 ) 2.2 Adjustment to regulatory liabilities 167.4 150.2 —
Unrecognized Tax Benefit Reconciliation	The following table presents a reconciliation of the beginning and ending balances of unrecognized tax benefits: Spire Spire Missouri 2020 2019 2018 2020 2019 2018 Unrecognized tax benefits, beginning of year $ 10.7 $ 8.1 $ 11.0 $ 10.4 $ 7.8 $ 10.7 Decrease related to tax law changes — — (4.0 ) — — (4.0 ) Increases related to tax positions taken in current year 2.6 4.5 1.2 2.6 4.5 1.1 Reductions related to tax positions taken in prior year — (1.9 ) — — (1.9 ) — Reductions due to lapse of applicable statute of limitations (0.1 ) — (0.1 ) — — — Unrecognized tax benefits, end of year $ 13.2 $ 10.7 $ 8.1 $ 13.0 $ 10.4 $ 7.8

Pension Plans and Other Postr_2

Pension Plans and Other Postretirement Benefits (Tables)	12 Months Ended
	Sep. 30, 2020
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements Of Plan Assets	The table below categorizes the fair value measurements of the Spire pension plan assets: Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total As of September 30, 2020 Cash and cash equivalents $ 11.5 $ — $ — $ 11.5 Equity funds - global (including U.S.) 31.4 195.6 — 227.0 Equity index funds - global (including U.S.) 32.6 — — 32.6 Debt securities: U.S. bond funds 48.9 — — 48.9 U.S. government index funds 78.3 — — 78.3 Global funds (including U.S.) — 74.8 — 74.8 Total $ 202.7 $ 270.4 $ — $ 473.1 As of September 30, 2019 Cash and cash equivalents $ 42.5 $ — $ — $ 42.5 Equity mutual funds - U.S. 40.5 17.0 — 57.5 Equity mutual funds - international 30.1 8.6 — 38.7 Debt securities: U.S. bond mutual funds 34.8 73.9 — 108.7 U.S. government 52.9 9.5 — 62.4 U.S. corporate 143.7 — — 143.7 U.S. municipal 4.0 — — 4.0 International 44.1 7.5 — 51.6 Derivatives and margin receivable 0.2 — — 0.2 103-12 Direct Filing Entities — 12.5 — 12.5 Total $ 392.8 $ 129.0 $ — $ 521.8 The table below categorizes the fair value measurements of Spire’s postretirement plan assets: Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total As of September 30, 2020 Cash and cash equivalents $ 3.6 $ — $ — $ 3.6 U.S. stock/bond mutual funds 199.4 72.2 — 271.6 International fund 1.0 14.8 — 15.8 Total $ 204.0 $ 87.0 $ — $ 291.0 As of September 30, 2019 Cash and cash equivalents $ 5.3 $ — $ — $ 5.3 U.S. stock/bond mutual funds 187.1 71.8 — 258.9 International fund 1.0 14.6 — 15.6 Total $ 193.4 $ 86.4 $ — $ 279.8
Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements Of Plan Assets	The table below categorizes the fair value measurements of Spire Missouri’s pension plan assets: Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total As of September 30, 2020 Cash and cash equivalents $ 9.5 $ — $ — $ 9.5 Equity funds - global (including U.S.) 22.1 137.8 — 159.9 Equity index funds - global (including U.S.) 22.8 — — 22.8 Debt securities: U.S. bond funds 31.0 — — 31.0 U.S. government index funds 59.6 — — 59.6 Global funds (including U.S.) — 53.4 — 53.4 Total $ 145.0 $ 191.2 $ — $ 336.2 As of September 30, 2019 Cash and cash equivalents $ 41.2 $ — $ — $ 41.2 Equity mutual funds - U.S. — 9.1 — 9.1 Equity mutual funds - international — 3.3 — 3.3 Debt securities: U.S. bond mutual funds — 73.9 — 73.9 U.S. government 52.9 6.8 — 59.7 U.S. corporate 143.7 — — 143.7 U.S. municipal 4.0 — — 4.0 International 44.1 — — 44.1 Derivatives and margin receivable 0.2 — — 0.2 Total $ 286.1 $ 93.1 $ — $ 379.2 The table below categorizes the fair value measurements of Spire Missouri’s postretirement plan assets: Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total As of September 30, 2020 Cash and cash equivalents $ 3.0 $ — $ — $ 3.0 U.S. stock/bond mutual funds 196.2 — — 196.2 Total $ 199.2 $ — $ — $ 199.2 As of September 30, 2019 Cash and cash equivalents $ 5.2 $ — $ — $ 5.2 U.S. stock/bond mutual funds 183.7 — — 183.7 Total $ 188.9 $ — $ — $ 188.9
Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value Measurements Of Plan Assets	The table below categorizes the fair value measurements of Spire Alabama’s pension plan assets: Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total As of September 30, 2020 Cash and cash equivalents $ 0.9 $ — $ — $ 0.9 Equity funds - global (including U.S.) 6.1 37.5 — 43.6 Equity index funds - global (including U.S.) 6.4 - — 6.4 Debt securities: U.S. bond funds 11.7 — — 11.7 U.S. government index funds 12.1 — — 12.1 Global funds (including U.S.) — 13.9 — 13.9 Total $ 37.2 $ 51.4 $ — $ 88.6 As of September 30, 2019 Cash and cash equivalents $ 0.8 $ — $ — $ 0.8 Equity mutual funds - U.S. 26.5 5.2 — 31.7 Equity mutual funds - international 19.7 3.5 — 23.2 Debt securities: U.S. bond mutual funds 22.8 — — 22.8 U.S. government — 1.7 — 1.7 International — 4.9 — 4.9 103-12 Direct Filing Entities — 8.2 — 8.2 Total $ 69.8 $ 23.5 $ — $ 93.3 The table below categorizes the fair value measurements of Spire Alabama’s postretirement plan assets: Quoted Prices in Active Markets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total As of September 30, 2020 U.S. stock/bond mutual funds $ — $ 72.2 $ — $ 72.2 International fund — 14.8 — 14.8 Total $ — $ 87.0 $ — $ 87.0 As of September 30, 2019 U.S. stock/bond mutual funds $ — $ 71.8 $ — $ 71.8 International fund — 14.6 — 14.6 Total $ — $ 86.4 $ — $ 86.4
Pension Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Net Periodic Cost	The net periodic pension costs include the following components: Spire Spire Missouri Spire Alabama 2020 2019 2018 2020 2019 2018 2020 2019 2018 Service cost – benefits earned during the period $ 22.5 $ 19.3 $ 20.2 $ 15.7 $ 12.4 $ 12.7 $ 6.1 $ 6.2 $ 6.4 Interest cost on projected benefit obligation 22.6 28.2 27.4 15.8 19.8 19.5 4.9 6.0 5.5 Expected return on plan assets (35.0 ) (36.3 ) (37.0 ) (24.6 ) (25.5 ) (27.2 ) (6.9 ) (7.3 ) (6.5 ) Amortization of prior service (credit) cost (2.5 ) (1.1 ) (0.9 ) 0.1 0.9 0.9 (2.4 ) (1.8 ) (1.8 ) Amortization of actuarial loss 14.4 9.3 10.9 11.3 8.7 9.4 3.1 0.8 1.5 Loss on lump-sum settlements and curtailments 31.6 — 18.6 26.6 — 16.1 5.0 — 2.4 Subtotal 53.6 19.4 39.2 44.9 16.3 31.4 9.8 3.9 7.5 Regulatory adjustment 6.6 39.6 37.4 3.9 31.8 32.1 1.8 6.9 4.5 Net pension cost $ 60.2 $ 59.0 $ 76.6 $ 48.8 $ 48.1 $ 63.5 $ 11.6 $ 10.8 $ 12.0
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income	Other changes in plan assets and pension benefit obligations recognized in other comprehensive income or loss include the following: Spire Spire Missouri Spire Alabama 2020 2019 2018 2020 2019 2018 2020 2019 2018 Current year actuarial loss (gain) $ 68.0 $ 90.9 $ (1.4 ) $ 37.8 $ 59.0 $ 2.2 $ 24.4 $ 26.3 $ (0.6 ) Amortization of actuarial loss (14.4 ) (9.3 ) (10.9 ) (11.3 ) (8.7 ) (9.4 ) (3.1 ) (0.8 ) (1.5 ) Acceleration of loss recognized due to settlement (31.7 ) — (18.5 ) (26.6 ) — (16.1 ) (5.1 ) — (2.4 ) Current year service credit (4.4 ) (10.2 ) (0.1 ) (4.4 ) (3.7 ) — — (6.5 ) — Transfer due to merger — — 0.1 — — 0.1 — — — Amortization of prior service credit (cost) 2.5 1.1 (2.9 ) (0.1 ) (0.9 ) (0.9 ) 2.4 1.8 — Amortization of transition asset — — 1.8 — — — — — 1.8 Subtotal 20.0 72.5 (31.9 ) (4.6 ) 45.7 (24.1 ) 18.6 20.8 (2.7 ) Regulatory adjustment (19.5 ) (71.7 ) 31.6 5.1 (44.9 ) 23.8 (18.6 ) (20.8 ) 2.7 Total recognized in OCI $ 0.5 $ 0.8 $ (0.3 ) $ 0.5 $ 0.8 $ (0.3 ) $ — $ — $ —
Reconciliation of the Beginning and Ending Balances of Benefit Obligation	The following table shows the reconciliation of the beginning and ending balances of the pension benefit obligation at September 30: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Benefit obligation, beginning of year $ 751.4 $ 664.6 $ 538.4 $ 473.3 $ 152.5 $ 136.3 Service cost 22.5 19.3 15.7 12.4 6.1 6.2 Interest cost 22.6 28.2 15.8 19.8 4.9 6.0 Actuarial loss (gain) 37.5 104.8 15.6 76.0 18.4 23.7 Plan amendments (4.4 ) (10.2 ) (4.4 ) (3.7 ) — (6.5 ) Settlement loss 16.5 — 16.5 — — — Settlement benefits paid (89.3 ) — (74.5 ) — (14.8 ) — Regular benefits paid (24.2 ) (55.3 ) (17.9 ) (39.4 ) (3.6 ) (13.2 ) Benefit obligation, end of year $ 732.6 $ 751.4 $ 505.2 $ 538.4 $ 163.5 $ 152.5 Accumulated benefit obligation, end of year $ 699.3 $ 712.9 $ 473.7 $ 500.2 $ 161.8 $ 152.3
Fair Value of Plan Assets	The following table sets forth the reconciliation of the beginning and ending balances of the fair value of plan assets at September 30: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Fair value of plan assets, beginning of year $ 521.8 $ 499.2 $ 379.2 $ 349.1 $ 93.3 $ 101.3 Actual return on plan assets 21.1 50.1 19.1 42.4 1.0 4.7 Employer contributions 43.7 27.8 30.3 27.1 12.7 0.5 Settlement benefits paid (89.3 ) — (74.5 ) — (14.8 ) — Regular benefits paid (24.2 ) (55.3 ) (17.9 ) (39.4 ) (3.6 ) (13.2 ) Fair value of plan assets, end of year $ 473.1 $ 521.8 $ 336.2 $ 379.2 $ 88.6 $ 93.3 Funded status of plans, end of year $ (259.5 ) $ (229.6 ) $ (169.0 ) $ (159.2 ) $ (74.9 ) $ (59.2 )
Amounts Recognized in Consolidated Balance Sheets	The following table sets forth the amounts recognized in the balance sheets at September 30: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Current liabilities $ (0.6 ) $ (0.5 ) $ (0.6 ) $ (0.5 ) $ — $ — Noncurrent liabilities (258.9 ) (229.1 ) (168.4 ) (158.7 ) (74.9 ) (59.2 ) Total $ (259.5 ) $ (229.6 ) $ (169.0 ) $ (159.2 ) $ (74.9 ) $ (59.2 ) Pre-tax amounts recognized in accumulated other comprehensive loss not yet recognized as components of net periodic pension cost consist of: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Net actuarial loss $ 235.6 $ 213.7 $ 152.9 $ 153.1 $ 78.1 $ 61.9 Prior service (credit) cost (25.6 ) (23.7 ) (2.8 ) 1.7 (21.1 ) (23.5 ) Subtotal 210.0 190.0 150.1 154.8 57.0 38.4 Adjustments for amounts included in regulatory assets (206.7 ) (187.1 ) (146.8 ) (151.9 ) (57.0 ) (38.4 ) Total $ 3.3 $ 2.9 $ 3.3 $ 2.9 $ — $ —
Pre-tax Amounts Expected to Amortized From Accumulated Other Comprehensive Loss Into Net Periodic Pension Cost	At September 30, 2020, the following pre-tax amounts are expected to be amortized from accumulated other comprehensive loss into net periodic pension cost during fiscal 2020: Spire Spire Missouri Spire Alabama Amortization of net actuarial loss $ 16.0 $ 11.4 $ 4.6 Amortization of prior service (credit) cost (3.2 ) (0.6 ) (2.4 ) Subtotal 12.8 10.8 2.2 Regulatory adjustment (12.5 ) (10.5 ) (2.2 ) Total $ 0.3 $ 0.3 $ —
Assumptions Used to Calculate Net Periodic Cost and Benefit Obligations	The assumptions used to calculate net periodic pension costs for Spire Missouri are as follows: 2020 2019 2018 Weighted average discount rate - Spire Missouri East plan 3.20% 4.30% 3.75% Weighted average discount rate - Spire Missouri West plan 3.15% 4.35% 3.70% Weighted average rate of future compensation increase 3.00% 3.00% 3.00% Expected long-term rate of return on plan assets 7.25% 7.50% 7.75% The assumptions used to calculate net periodic pension costs for Spire Alabama are as follows: 2020 2019 2018 Weighted average discount rate 3.25%/3.20% 4.35% 3.65%/3.70% Weighted average rate of future compensation increase 3.00% 3.00% 3.00% Expected long-term rate of return on plan assets 7.25% 7.25% 7.25% The assumptions used to calculate the benefit obligations are as follows: 2020 2019 Weighted average discount rate - Spire Missouri East plan 2.85% 3.20% Weighted average discount rate - Spire Missouri West plan 2.75% 3.15% Weighted average discount rate - Spire Alabama plans 2.95%/2.80% 3.20%/3.25% Weighted average rate of future compensation increase 3.00% 3.00%
Projected Benefit Obligation, Accumulated Benefit Obligation, and Fair Value of Plan Assets for Plans That Have Projected Benefit Obligation and Accumulated Benefit Obligation in Excess of Plan Assets	Following are the year-end projected benefit obligation, accumulated benefit obligation, and fair value of plan assets for plans that have a projected benefit obligation and an accumulated benefit obligation in excess of plan assets: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Projected benefit obligation $ 732.6 $ 751.4 $ 505.2 $ 538.4 $ 163.5 $ 152.5 Accumulated benefit obligation 699.3 712.9 473.7 500.2 161.8 152.3 Fair value of plan assets 473.1 521.8 336.2 379.2 88.6 93.3
Targeted and Actual Plan Assets by Category	Following are the targeted and actual plan assets by category as of September 30 of each year for Spire Missouri and Spire Alabama: Spire Missouri 2020 Target 2020 Actual 2019 Target 2019 Actual Return seeking assets 70.0 % 70.0 % 56.5 % 57.0 % Liability hedging assets 30.0 % 27.0 % 43.5 % 39.8 % Other — % 3.0 % — % 3.2 % Total 100.0 % 100.0 % 100.0 % 100.0 % Spire Alabama 2020 Target 2020 Actual 2019 Target 2019 Actual Return seeking assets 70.0 % 71.0 % 60.0 % 58.5 % Liability hedging assets 30.0 % 27.0 % 29.0 % 29.8 % Other* — 2.0 % 11.0 % 11.7 % Total 100.0 % 100.0 % 100.0 % 100.0 %
Expected Benefit Payments for Succeeding Five Fiscal Years	Following are expected pension benefit payments for the succeeding five fiscal years, and in aggregate for the five fiscal years thereafter, for Spire, Spire Missouri, and Spire Alabama: 2021 2022 2023 2024 2025 2026- 2030 Spire $ 65.6 $ 64.1 $ 60.8 $ 58.6 $ 54.4 $ 246.0 Spire Missouri 49.1 45.6 43.3 41.9 37.7 168.7 Spire Alabama 13.5 15.4 14.3 13.5 13.3 59.0
Other Postretirement Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Net Periodic Cost	Net periodic postretirement benefit costs consist of the following components: Spire Spire Missouri Spire Alabama 2020 2019 2018 2020 2019 2018 2020 2019 2018 Service cost – benefits earned during the period $ 5.9 $ 7.4 $ 9.4 $ 5.3 $ 6.8 $ 9.0 $ 0.4 $ 0.4 $ 0.2 Interest cost on accumulated postretirement benefit obligation 6.3 9.0 8.6 4.7 6.9 6.9 1.4 1.8 1.5 Expected return on plan assets (16.7 ) (16.2 ) (13.9 ) (11.4 ) (11.1 ) (9.6 ) (5.0 ) (4.8 ) (4.1 ) Amortization of prior service (credit) cost (0.5 ) (0.1 ) (0.1 ) (0.2 ) 0.3 0.3 (0.3 ) (0.4 ) (0.4 ) Amortization of actuarial (gain) loss (2.0 ) (0.5 ) 0.8 (2.0 ) (0.5 ) 0.9 — — (0.1 ) Subtotal (7.0 ) (0.4 ) 4.8 (3.6 ) 2.4 7.5 (3.5 ) (3.0 ) (2.9 ) Regulatory adjustment 16.0 10.0 2.2 17.7 11.7 3.9 (1.8 ) (1.8 ) (1.8 ) Net postretirement benefit cost $ 9.0 $ 9.6 $ 7.0 $ 14.1 $ 14.1 $ 11.4 $ (5.3 ) $ (4.8 ) $ (4.7 )
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income	Other changes in plan assets and postretirement benefit obligations recognized in OCI include the following: Spire Spire Missouri Spire Alabama 2020 2019 2018 2020 2019 2018 2020 2019 2018 Current year actuarial (gain) loss $ (7.3 ) $ (12.2 ) $ (45.1 ) $ (7.6 ) $ (17.3 ) $ (47.1 ) $ 1.1 $ 5.5 $ 1.6 Amortization of actuarial gain (loss) 2.0 0.5 (0.8 ) 2.0 0.5 (0.9 ) — — 0.1 Current year prior service credit (cost) 15.8 5.5 — 9.5 4.9 — 6.3 0.6 — Amortization of current year service cost — 0.4 — — — — — 0.4 — Amortization of prior service (cost) credit 0.5 (0.3 ) 0.1 0.2 (0.3 ) (0.3 ) 0.3 — 0.4 Subtotal 11.0 (6.1 ) (45.8 ) 4.1 (12.2 ) (48.3 ) 7.7 6.5 2.1 Regulatory adjustment (11.0 ) 6.1 45.8 (4.1 ) 12.2 48.3 (7.7 ) (6.5 ) (2.1 ) Total recognized in OCI $ — $ — $ — $ — $ — $ — $ — $ — $ —
Reconciliation of the Beginning and Ending Balances of Benefit Obligation	The following table sets forth the reconciliation of the beginning and ending balances of the postretirement benefit obligation at September 30: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Benefit obligation, beginning of year $ 197.3 $ 208.1 $ 147.9 $ 158.8 $ 43.4 $ 43.1 Service cost 5.9 7.4 5.3 6.8 0.4 0.4 Interest cost 6.3 9.0 4.7 6.9 1.4 1.8 Actuarial (gain) loss 0.2 (18.9 ) 1.7 (19.5 ) (0.7 ) 1.2 Plan amendments 15.8 5.5 9.5 4.9 6.3 0.6 Retiree drug subsidy program — 0.2 — 0.2 — — Benefits paid (13.2 ) (14.0 ) (10.7 ) (10.2 ) (2.5 ) (3.7 ) Benefit obligation, end of year $ 212.3 $ 197.3 $ 158.4 $ 147.9 $ 48.3 $ 43.4
Fair Value of Plan Assets	The following table sets forth the reconciliation of the beginning and ending balances of the fair value of plan assets at September 30: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Fair value of plan assets at beginning of year $ 279.8 $ 283.5 $ 188.9 $ 189.5 $ 86.4 $ 89.6 Actual return on plan assets 24.2 9.7 20.8 9.0 3.1 0.5 Employer contributions 0.2 0.6 0.2 0.6 — — Benefits paid (13.2 ) (14.0 ) (10.7 ) (10.2 ) (2.5 ) (3.7 ) Fair value of plan assets, end of year $ 291.0 $ 279.8 $ 199.2 $ 188.9 $ 87.0 $ 86.4 Funded status of plans, end of year $ 78.7 $ 82.5 $ 40.8 $ 41.0 $ 38.7 $ 43.0
Amounts Recognized in Consolidated Balance Sheets	The following table sets forth the amounts recognized in the balance sheets at September 30: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Noncurrent assets $ 129.0 $ 118.3 $ 90.3 $ 75.3 $ 38.7 $ 43.0 Current liabilities (0.5 ) (0.5 ) (0.5 ) (0.5 ) — — Noncurrent liabilities (49.8 ) (35.3 ) (49.0 ) (33.8 ) — — Total $ 78.7 $ 82.5 $ 40.8 $ 41.0 $ 38.7 $ 43.0 Pre-tax amounts recognized in accumulated other comprehensive loss not yet recognized as components of net periodic postretirement benefit cost consist of: Spire Spire Missouri Spire Alabama 2020 2019 2020 2019 2020 2019 Net actuarial gain $ (61.7 ) $ (56.3 ) $ (58.3 ) $ (52.6 ) $ (1.5 ) $ (2.6 ) Prior service (credit) cost 15.5 (1.0 ) 10.4 0.6 5.1 (1.6 ) Subtotal (46.2 ) (57.3 ) (47.9 ) (52.0 ) 3.6 (4.2 ) Adjustments for amounts included in regulatory assets 46.2 57.3 47.9 52.0 (3.6 ) 4.2 Total $ — $ — $ — $ — $ — $ —
Pre-tax Amounts Expected to Amortized From Accumulated Other Comprehensive Loss Into Net Periodic Pension Cost	At September 30, 2020, the following pre-tax amounts are expected to be amortized from accumulated other comprehensive loss into net periodic postretirement benefit cost during fiscal 2020: Spire Spire Missouri Spire Alabama Amortization of net actuarial gain $ (1.6 ) $ (1.5 ) $ — Amortization of prior service credit 1.0 0.7 0.3 Subtotal (0.6 ) (0.8 ) 0.3 Regulatory adjustment 0.6 0.8 (0.3 ) Total $ — $ — $ —
Assumptions Used to Calculate Net Periodic Cost and Benefit Obligations	The assumptions used to calculate net periodic postretirement benefit costs for Spire Missouri are as follows: 2020 2019 2018 Weighted average discount rate - Spire Missouri plans 3.15% 4.30% 3.60% Weighted average rate of future compensation increase 3.00% 3.00% 3.00% Expected long-term rate of return on plan assets - Spire Missouri plans 6.25% 6.25% 5.75%/7.75% The assumptions used to calculate net periodic postretirement benefit costs for Spire Alabama are as follows: 2020 2019 2018 Weighted average discount rate 3.15% 4.30% 3.80% Expected long-term rate of return on plan assets 5.00%/6.25% 5.00%/6.25% 3.75%/6.00% The assumptions used to calculate the accumulated postretirement benefit obligations are as follows: 2020 2019 Weighted average discount rate - Spire Alabama plans 2.75% 3.15% Weighted average discount rate - Spire Missouri plans 2.75% 3.15% Weighted average rate of future compensation increase - Spire Missouri East plans 3.00% 3.00%
Targeted and Actual Plan Assets by Category	Following are the targeted and actual plan assets by category as of September 30 of each year for Spire Missouri and Spire Alabama: Spire Missouri Target 2020 Actual 2019 Actual Equity securities 60.0 % 57.4 % 58.4 % Debt securities 40.0 % 37.8 % 38.8 % Other (cash and cash equivalents held to make benefit payments) — % 4.8 % 2.8 % Total 100.0 % 100.0 % 100.0 % Spire Alabama Target 2020 Actual 2019 Actual Equity securities 60.0 % 61.8 % 60.3 % Debt securities 40.0 % 38.2 % 39.7 % Total 100.0 % 100.0 % 100.0 %
Expected Benefit Payments for Succeeding Five Fiscal Years	Following are expected postretirement benefit payments for the succeeding five fiscal years, and in aggregate for the five fiscal years thereafter for Spire, Spire Missouri, and Spire Alabama: 2021 2022 2023 2024 2025 2026- 2030 Spire $ 14.7 $ 15.4 $ 16.1 $ 16.5 $ 16.6 $ 78.2 Spire Missouri 11.7 12.3 12.9 13.2 13.3 61.7 Spire Alabama 2.7 2.8 2.9 3.0 3.0 14.2
Assumed Medical Cost Trend Rates and Effect of An Assumed 1% Changed in Assumed Medical Cost Trend.	The assumed medical cost trend rates at September 30 are as follows: 2020 2019 Medical cost trend assumed for next year - Spire Missouri 6.50% 6.75% Medical cost trend assumed for next year - Spire Alabama 6.50% 6.75% Rate to which the medical cost trend rate is assumed to decline (the ultimate medical cost trend rate) 5.00% 5.00% Year the rate reaches the ultimate trend 2025 2025 The following table presents the effects of an assumed 1% change in the assumed medical cost trend rate: Spire Spire Missouri Spire Alabama 1% Increase 1% Decrease 1% Increase 1% Decrease 1% Increase 1% Decrease Net periodic postretirement benefit cost $ 0.8 $ (0.7 ) $ 0.6 $ (0.6 ) $ 0.2 $ (0.1 ) Accumulated postretirement benefit obligation 9.7 (8.7 ) 6.5 (5.9 ) 2.6 (2.3 )

Information by Operating Segm_2

Information by Operating Segment (Tables)	12 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Schedule of Operating Segment Information	2020 Gas Utility Gas Marketing Other Eliminations Consolidated Revenues from external customers $ 1,751.8 $ 87.9 $ 15.7 $ — $ 1,855.4 Intersegment revenues 0.2 — 42.1 (42.3 ) — Total Operating Revenues 1,752.0 87.9 57.8 (42.3 ) 1,855.4 Operating Expenses Natural gas 660.2 65.1 0.4 (29.6 ) 696.1 Other operation and maintenance 421.3 11.8 38.2 (12.7 ) 458.6 Depreciation and amortization 189.7 0.6 7.0 — 197.3 Taxes, other than income taxes 146.5 1.1 0.8 — 148.4 Impairments — — 148.6 — 148.6 Total Operating Expenses 1,417.7 78.6 195.0 (42.3 ) 1,649.0 Operating Income (Loss) $ 334.3 $ 9.3 $ (137.2 ) $ — $ 206.4 Net Economic Earnings (Loss) $ 213.4 $ 9.1 $ (14.7 ) $ — $ 207.8 Capital Expenditures $ 547.8 $ 3.6 $ 87.0 $ — $ 638.4 2019 Gas Utility Gas Marketing Other Eliminations Consolidated Revenues from external customers $ 1,859.2 $ 83.7 $ 9.5 $ — $ 1,952.4 Intersegment revenues 1.6 — 12.0 (13.6 ) — Total Operating Revenues 1,860.8 83.7 21.5 (13.6 ) 1,952.4 Operating Expenses Natural gas 794.6 47.9 0.5 (2.7 ) 840.3 Other operation and maintenance 441.7 11.7 31.6 (10.9 ) 474.1 Depreciation and amortization 179.4 0.1 2.2 — 181.7 Taxes, other than income taxes 151.7 0.8 1.5 — 154.0 Total Operating Expenses 1,567.4 60.5 35.8 (13.6 ) 1,650.1 Operating Income (Loss) $ 293.4 $ 23.2 $ (14.3 ) $ — $ 302.3 Net Economic Earnings (Loss) $ 199.8 $ 19.4 $ (24.1 ) $ — $ 195.1 Capital Expenditures $ 565.4 $ 3.1 $ 254.8 $ — $ 823.3 2018 Gas Utility Gas Marketing Other Eliminations Consolidated Revenues from external customers $ 1,888.0 $ 71.6 $ 5.4 $ — $ 1,965.0 Intersegment revenues 0.4 — 11.1 (11.5 ) — Total Operating Revenues 1,888.4 71.6 16.5 (11.5 ) 1,965.0 Operating Expenses Natural gas 842.6 30.2 0.3 (1.4 ) 871.7 Other operation and maintenance 449.7 7.4 30.3 (10.1 ) 477.3 Depreciation and amortization 167.0 — 1.4 — 168.4 Taxes, other than income taxes 152.5 0.2 0.8 — 153.5 Total Operating Expenses 1,611.8 37.8 32.8 (11.5 ) 1,670.9 Operating Income (Loss) $ 276.6 $ 33.8 $ (16.3 ) $ — $ 294.1 Net Economic Earnings (Loss) $ 183.1 $ 22.9 $ (22.3 ) $ — $ 183.7 Capital Expenditures $ 457.7 $ — $ 41.7 $ — $ 499.4 Total Assets at End of Year 2020 2019 2018 Gas Utility $ 6,716.2 $ 6,094.6 $ 5,606.7 Gas Marketing 182.7 212.3 295.3 Other 2,443.5 2,692.7 2,508.0 Eliminations (1,101.2 ) (1,380.4 ) (1,566.4 ) Total Assets $ 8,241.2 $ 7,619.2 $ 6,843.6
Schedule of Reconciliation of Consolidated Net Economic Earnings to Consolidated Net Income	Reconciliation of Consolidated Net Income to Consolidated Net Economic Earnings 2020 2019 2018 Net Income $ 88.6 $ 184.6 $ 214.2 Adjustments, pre-tax: Impairments 148.6 — — Provision for ISRS rulings — 12.2 — Missouri regulatory adjustments — — 30.6 Fair value and timing adjustments 2.5 1.2 (4.3 ) Acquisition, divestiture and restructuring activities — 0.4 13.6 Income tax effect of adjustments (31.9 ) (3.3 ) (10.3 ) Effect of the Tax Cuts and Jobs Act — — (60.1 ) Net Economic Earnings $ 207.8 $ 195.1 $ 183.7

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Sep. 30, 2020
Regulated Operations [Abstract]
Schedule of Regulatory Assets and Liabilities	The following regulatory assets and regulatory liabilities were reflected in the Balance Sheets as of September 30, 2020 and 2019. Spire Spire Missouri Spire Alabama September 30 2020 2019 2020 2019 2020 2019 Regulatory Assets: Current: Pension and postretirement benefit costs $ 30.6 $ 30.1 $ 21.9 $ 21.9 $ 7.7 $ 7.3 Unamortized purchased gas adjustments 5.5 18.2 — — 5.5 17.7 Other 33.4 30.3 10.2 7.5 7.2 8.9 Total Current Regulatory Assets 69.5 78.6 32.1 29.4 20.4 33.9 Noncurrent: Future income taxes due from customers 123.5 111.0 114.6 102.9 2.2 2.2 Pension and postretirement benefit costs 439.3 416.6 332.6 333.3 98.2 77.2 Cost of removal 395.6 150.9 7.1 — 388.6 150.9 Unamortized purchased gas adjustments 12.1 9.1 12.1 9.1 — — Energy efficiency 39.6 35.0 39.6 35.0 — — Other 59.3 45.0 42.7 27.2 0.9 0.9 Total Noncurrent Regulatory Assets 1,069.4 767.6 548.7 507.5 489.9 231.2 Total Regulatory Assets $ 1,138.9 $ 846.2 $ 580.8 $ 536.9 $ 510.3 $ 265.1 Regulatory Liabilities: Current: Pension and postretirement benefit costs $ 5.8 $ 5.8 $ 3.6 $ 3.6 $ 2.2 $ 2.2 Unamortized purchased gas adjustments 73.1 26.2 72.3 25.4 — — Other 34.1 28.8 27.3 23.3 1.7 1.2 Total Current Regulatory Liabilities 113.0 60.8 103.2 52.3 3.9 3.4 Noncurrent: Deferred taxes due to customers 138.8 179.8 121.4 162.5 — — Pension and postretirement benefit costs 157.6 142.3 140.4 119.1 14.8 19.1 Accrued cost of removal 28.6 41.6 — 15.7 — — Unamortized purchased gas adjustments 4.4 — 4.4 — — — Other 14.3 35.3 8.6 29.2 3.7 3.9 Total Noncurrent Regulatory Liabilities 343.7 399.0 274.8 326.5 18.5 23.0 Total Regulatory Liabilities $ 456.7 $ 459.8 $ 378.0 $ 378.8 $ 22.4 $ 26.4
Schedule of Regulatory Assets Not Earning a Return	A portion of the Company’s regulatory assets are not earning a return and are shown in the schedule below: Spire Spire Missouri September 30 2020 2019 2020 2019 Pension and postretirement benefit costs $ 232.3 $ 211.1 $ 232.3 $ 211.1 Future income taxes due from customers 121.3 108.8 114.6 102.9 Other 12.9 14.3 12.9 14.3 Total Regulatory Assets Not Earning a Return $ 366.5 $ 334.2 $ 359.8 $ 328.3

Leases (Tables)

Leases (Tables)	12 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Operating Lease Cost Cash Flow and Noncash Information	Operating lease cost, cash flow and noncash information for the year ended September 30, 2020, are shown in the following table. Spire Spire Missouri Spire Alabama Operating lease cost, including amounts capitalized $ 8.7 $ 0.5 $ 3.5 Cash flow and noncash information about operating leases: Operating cash flows representing cash paid for amounts included in the measurement of lease liabilities 8.5 0.5 3.3 Right-of-use assets obtained in exchange for lease liabilities 71.1 2.1 10.0
Summary of Balance Sheet and Weighted-Average Information about Operating Leases	The following table shows balance sheet and weighted-average information about operating leases as of September 30, 2020. Balance sheet classification Spire Spire Missouri Spire Alabama Right-of-use assets Deferred Charges and Other Assets: Other $ 65.1 $ 1.7 $ 6.7 Lease liabilities, current Current Liabilities, Other 6.5 0.3 1.9 Lease liabilities, noncurrent Deferred Credits and Other Liabilities: Other 58.4 1.4 4.7 Weighted-average remaining lease term 15.9 years 5.3 years 3.3 years Weighted-average discount rate 4.2 % 2.5 % 2.2 %
Schedule of Maturity Analysis for Operating Lease Liabilities	Following is a maturity analysis by fiscal year for operating lease liabilities as of September 30, 2020. Spire Spire Missouri Spire Alabama 2021 $ 6.6 $ 0.3 $ 1.9 2022 7.2 0.4 2.1 2023 7.2 0.3 2.1 2024 5.8 0.3 0.7 2025 5.1 0.3 — Thereafter 58.4 0.2 — Total undiscounted lease payments 90.3 1.8 6.8 Less present value discount (25.4 ) (0.1 ) (0.2 ) Total current and noncurrent lease liabilities $ 64.9 $ 1.7 $ 6.6
Schedule of Annual Minimum Rental Commitments for Operating Leases	The aggregate rental expense for fiscal years 2018 and 2019 and the annual minimum rental commitments for all leases having an initial or remaining non-cancelable term of more than one year as of September 30, 2019, were as follows (under ASC 840). Aggregate Rental Expense Minimum Rental Commitments as of September 30, 2019 2018 2019 2020 2021 2022 2023 2024 Later Total Spire $ 10.0 $ 10.9 $ 8.2 $ 7.0 $ 6.8 $ 6.1 $ 4.8 $ 36.5 $ 69.4 Spire Missouri 3.6 3.7 0.5 0.2 — — — — 0.7 Spire Alabama 4.7 5.2 2.9 2.1 2.1 2.1 0.7 — 9.9

Interim Financial Information_2

Interim Financial Information (Unaudited) (Tables)	12 Months Ended
	Sep. 30, 2020
Quarterly Financial Information [Line Items]
Schedule of Quarterly Financial Information	Three Months Ended Dec. 31 March 31 June 30 Sept. 30 Fiscal Year 2020 Total Operating Revenues $ 566.9 $ 715.5 $ 321.1 $ 251.9 Operating Income (Loss) 102.3 210.5 (106.5 ) 0.1 Net Income (Loss) 67.0 133.6 (92.3 ) (19.7 ) Basic Earnings (Loss) Per Share of Common Stock $ 1.24 $ 2.55 $ (1.87 ) $ (0.45 ) Diluted Earnings (Loss) Per Share of Common Stock $ 1.24 $ 2.54 $ (1.87 ) $ (0.45 ) Fiscal Year 2019 Total Operating Revenues $ 602.0 $ 803.5 $ 321.3 $ 225.6 Operating Income (Loss) 105.1 209.5 13.3 (25.6 ) Net Income (Loss) 67.3 154.6 (3.0 ) (34.3 ) Basic Earnings (Loss) Per Share of Common Stock $ 1.33 $ 3.05 $ (0.09 ) $ (0.75 ) Diluted Earnings (Loss) Per Share of Common Stock $ 1.32 $ 3.04 $ (0.09 ) $ (0.74 )
Spire Missouri
Quarterly Financial Information [Line Items]
Schedule of Quarterly Financial Information	Three Months Ended Dec. 31 March 31 June 30 Sept. 30 Fiscal Year 2020 Total Operating Revenues $ 374.0 $ 457.5 $ 203.9 $ 158.2 Operating Income 67.0 117.7 7.0 13.9 Net Income 48.0 74.5 6.5 1.2 Fiscal Year 2019 Total Operating Revenues $ 413.2 $ 556.6 $ 191.4 $ 130.6 Operating Income (Loss) 71.4 102.4 12.2 (11.2 ) Net Income (Loss) 51.2 80.0 1.1 (17.3 )
Spire Alabama
Quarterly Financial Information [Line Items]
Schedule of Quarterly Financial Information	Three Months Ended Dec. 31 March 31 June 30 Sept. 30 Fiscal Year 2020 Total Operating Revenues $ 126.2 $ 185.5 $ 81.2 $ 62.1 Operating Income (Loss) 20.9 81.2 9.3 (8.5 ) Net Income (Loss) 13.2 57.8 3.6 (8.9 ) Fiscal Year 2019 Total Operating Revenues $ 133.5 $ 180.4 $ 90.8 $ 60.8 Operating Income (Loss) 17.1 79.6 11.1 (12.3 ) Net Income (Loss) 10.3 56.7 5.6 (12.3 )

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	1 Months Ended			3 Months Ended	12 Months Ended
	Oct. 31, 2018USD ($)	May 31, 2018USD ($)	Dec. 31, 2017USD ($)	Jun. 30, 2020USD ($)Station	Sep. 30, 2020USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2020USD ($)ReportingUnit	Sep. 30, 2020USD ($)	Sep. 30, 2020USD ($)operating-segment	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2020USD ($)	Oct. 25, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Number of reportable segments							2		2
Revisions in estimated cash flows						$ 192,400,000				$ 1,000,000
Difference between replacement cost of gas storage and inventory basis amount						12,500,000				17,000,000
Goodwill					$ 1,171,600,000	1,171,600,000	$ 1,171,600,000	$ 1,171,600,000	$ 1,171,600,000	1,171,600,000
Goodwill accumulated impairment loss					$ 0	0	0	0	0
Impairment charge of long-lived assets						148,600,000				$ 0	$ 0
Number of months of the original maturity of debt instruments purchased					3 months
Restricted cash											17,000,000
ASU 2017-07
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reclassification of net periodic benefit costs (income) to other income (expense)											$ 14,400,000
ASU 2016-13 | Scenario Forecast
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Credit loss allowances for available-for-sale securities recognized at adoption of ASU												$ 0
Gas Utility
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Goodwill					$ 210,200,000	210,200,000	210,200,000	210,200,000	210,200,000
Gas Marketing
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Goodwill					$ 0	$ 0	$ 0	$ 0	$ 0
Natural Gas Storage Facility
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Percentage of voting interest acquired	20.00%	100.00%	80.00%
Consideration	$ 17,000,000	$ 12,200,000	$ 24,800,000
Payments to acquire business			16,000,000
Non-interest-bearing note			10,000,000
Non-interest-bearing note, value			$ 8,800,000
Percentage of voting interest													20.00%
Spire Missouri
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Average annual depreciation and amortization expense percentage					2.90%	2.90%	2.90%	2.90%	2.90%	3.00%	3.00%
Revisions in estimated cash flows						$ (25,900,000)				$ (2,800,000)
Goodwill					$ 210,200,000	210,200,000	$ 210,200,000	$ 210,200,000	$ 210,200,000	210,200,000
Spire Missouri | ASU 2017-07
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reclassification of net periodic benefit costs (income) to other income (expense)											$ 17,200,000
Spire Missouri | ASU 2016-13 | Scenario Forecast
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Credit loss allowances for available-for-sale securities recognized at adoption of ASU												0
Spire Missouri | Affiliated Entity | Spire Marketing | Regulated Operation
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Purchases of natural gas from related party						56,900,000				95,300,000	71,500,000
Sales of natural gas to Spire Marketing Inc.						100,000				$ 1,700,000	$ 300,000
Spire Alabama
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Composite depreciation rate								3.10%		3.10%	3.10%
Revisions in estimated cash flows						221,100,000				$ 0
Finance receivable, net					$ 9,400,000	$ 9,400,000	$ 9,400,000	$ 9,400,000	$ 9,400,000	11,700,000
Threshold period past due for collection					90 days
Threshold period past due for write-off of financing receivable					12 months	12 months	12 months	12 months	12 months
Spire Alabama | ASU 2017-07
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reclassification of net periodic benefit costs (income) to other income (expense)											$ (2,000,000)
Spire Alabama | ASU 2016-13 | Scenario Forecast
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Credit loss allowances for available-for-sale securities recognized at adoption of ASU												$ 0
Spire Alabama | Financing Receivables, Equal to Greater than 90 Days Past Due
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Finance receivable 90 days past due					$ 300,000	$ 300,000	$ 300,000	$ 300,000	$ 300,000	$ 400,000
Spire Alabama | Affiliated Entity | Spire Marketing | Regulated Operation
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Purchases of natural gas from related party						6,300,000
Sales of natural gas to Spire Marketing Inc.						$ 300,000
Spire Storage West LLC ("Spire Storage") | Non-Utility Property
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Impairment charge of long-lived assets				$ 140,800,000
Number of commercial stations impaired | Station				2
Spire Storage West LLC ("Spire Storage") | Two Compressed Natural Gas Fueling Stations (Non-utility Property)
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Impairment charge of long-lived assets				$ 7,800,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Accrued Capital Expenditures (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Schedule Of Accrued Capital Expenditures Excluded From Statement Of Cash Flow [Line Items]
Accruals for capital expenditures	$ 67.6	$ 80.6	$ 62.1
Spire Missouri
Schedule Of Accrued Capital Expenditures Excluded From Statement Of Cash Flow [Line Items]
Accruals for capital expenditures	34.3	40.1	36.7
Spire Alabama
Schedule Of Accrued Capital Expenditures Excluded From Statement Of Cash Flow [Line Items]
Accruals for capital expenditures	$ 17	$ 11.9	$ 8.9

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Asset Retirement Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Asset retirement obligations [Roll forward]
Asset retirement obligations, beginning of year	$ 337.6	$ 321.1
Liabilities incurred during the period	3	10.8
Liabilities settled during the period	(6.9)	(8.3)
Accretion	14	13
Revisions in estimated cash flows	192.4	1
Asset retirement obligations, end of year	540.1	337.6
Spire Missouri
Asset retirement obligations [Roll forward]
Asset retirement obligations, beginning of year	173.5	174.1
Liabilities incurred during the period	2.6	1.6
Liabilities settled during the period	(4)	(6.8)
Accretion	7.2	7.4
Revisions in estimated cash flows	(25.9)	(2.8)
Asset retirement obligations, end of year	153.4	173.5
Spire Alabama
Asset retirement obligations [Roll forward]
Asset retirement obligations, beginning of year	148.7	135.7
Liabilities incurred during the period	0	8.8
Liabilities settled during the period	(1.6)	(0.8)
Accretion	6.1	5
Revisions in estimated cash flows	221.1	0
Asset retirement obligations, end of year	$ 374.3	$ 148.7

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Schedule of Inter-Company Transactions (Details) - Affiliated Entity - Spire Missouri - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Spire Marketing | Regulated Operation
Related Party Transaction [Line Items]
Purchases of natural gas from related party	$ 56.9	$ 95.3	$ 71.5
Sales of natural gas to Spire Marketing Inc.	0.1	1.7	0.3
Spire STL Pipeline LLC | Unregulated Operation
Related Party Transaction [Line Items]
Transportation services received	27.9
Spire NGL Inc. | Unregulated Operation
Related Party Transaction [Line Items]
Transportation services received	$ 1	$ 1	$ 1

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Schedule of Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance at beginning of year	$ 23	$ 22.4	$ 18.3
Additions charged to expense	14	16.9	14.6
Net deductions	(12.1)	(16.3)	(10.5)
Allowance at end of year	24.9	23	22.4
Spire Missouri
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance at beginning of year	14.9	16	14.1
Additions charged to expense	12.7	12.3	11.9
Net deductions	(9.5)	(13.4)	(10)
Allowance at end of year	18.1	14.9	16
Spire Alabama
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance at beginning of year	6.3	3.9	2.6
Additions charged to expense	0.9	4.7	2.1
Net deductions	(1.7)	(2.3)	(0.8)
Allowance at end of year	$ 5.5	$ 6.3	$ 3.9

Revenue - Schedule of Revenue D

Revenue - Schedule of Revenue Disaggregated by Source and Customer Type (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disaggregation Of Revenue [Line Items]
Total operating revenues	$ 251.9	$ 321.1	$ 715.5	$ 566.9	$ 225.6	$ 321.3	$ 803.5	$ 602	$ 1,855.4	$ 1,952.4	$ 1,965
Intersegment Eliminations
Disaggregation Of Revenue [Line Items]
Total operating revenues									(42.3)	(13.6)	(11.5)
Gas Utility
Disaggregation Of Revenue [Line Items]
Total operating revenues									1,751.8	1,859.2	1,888
Gas Utility | Operating Segments
Disaggregation Of Revenue [Line Items]
Total operating revenues									1,752	1,860.8	1,888.4
Gas Utility | Intersegment Eliminations
Disaggregation Of Revenue [Line Items]
Total operating revenues									0.2	1.6	0.4
Gas Marketing
Disaggregation Of Revenue [Line Items]
Total operating revenues									87.9	83.7	71.6
Gas Marketing | Operating Segments
Disaggregation Of Revenue [Line Items]
Total operating revenues									87.9	83.7	$ 71.6
Spire
Disaggregation Of Revenue [Line Items]
Total operating revenues									1,855.4	1,952.4
Spire | Operating Segments
Disaggregation Of Revenue [Line Items]
Total operating revenues									1,897.7	1,966
Spire | Intersegment Eliminations
Disaggregation Of Revenue [Line Items]
Total operating revenues									(42.3)	(13.6)
Spire | Gas Utility | Operating Segments
Disaggregation Of Revenue [Line Items]
Total operating revenues									1,747.7	1,877.7
Changes in accrued revenue under alternative revenue programs									4.3	(16.9)
Total operating revenues									1,752	1,860.8
Spire | Gas Utility | Operating Segments | Residential
Disaggregation Of Revenue [Line Items]
Total operating revenues									1,184.3	1,267.3
Spire | Gas Utility | Operating Segments | Commercial & Industrial
Disaggregation Of Revenue [Line Items]
Total operating revenues									383	433.9
Spire | Gas Utility | Operating Segments | Transportation
Disaggregation Of Revenue [Line Items]
Total operating revenues									115.8	112.1
Spire | Gas Utility | Operating Segments | Off-system & Other Incentive
Disaggregation Of Revenue [Line Items]
Total operating revenues									38.4	41.9
Spire | Gas Utility | Operating Segments | Other Customer Revenue
Disaggregation Of Revenue [Line Items]
Total operating revenues									26.2	22.5
Spire | Gas Marketing | Operating Segments
Disaggregation Of Revenue [Line Items]
Total operating revenues									87.9	83.7
Spire | Gas Marketing | Operating Segments | Revenue From Contracts With Retail Customers
Disaggregation Of Revenue [Line Items]
Total operating revenues									87.9	83.7
Spire | Other | Operating Segments
Disaggregation Of Revenue [Line Items]
Total operating revenues									$ 57.8	$ 21.5

Revenue - Schedule of Operating

Revenue - Schedule of Operating Revenue Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disaggregation Of Revenue [Line Items]
Total operating revenues	$ 251.9	$ 321.1	$ 715.5	$ 566.9	$ 225.6	$ 321.3	$ 803.5	$ 602	$ 1,855.4	$ 1,952.4	$ 1,965
Spire Missouri
Disaggregation Of Revenue [Line Items]
Total operating revenues									1,191.3	1,304.7
Changes in accrued revenue under alternative revenue programs									2.3	(12.9)
Total operating revenues	158.2	203.9	457.5	374	130.6	191.4	556.6	413.2	1,193.6	1,291.8	1,285.6
Spire Missouri | Residential
Disaggregation Of Revenue [Line Items]
Total operating revenues									859.6	945.9
Spire Missouri | Commercial & Industrial
Disaggregation Of Revenue [Line Items]
Total operating revenues									241.4	283.8
Spire Missouri | Transportation
Disaggregation Of Revenue [Line Items]
Total operating revenues									32.9	33.1
Spire Missouri | Off-system & Other Incentive
Disaggregation Of Revenue [Line Items]
Total operating revenues									35.1	41.9
Spire Missouri | Other Customer Revenue
Disaggregation Of Revenue [Line Items]
Total operating revenues									22.3
Spire Alabama
Disaggregation Of Revenue [Line Items]
Total operating revenues									455.2	469
Changes in accrued revenue under alternative revenue programs									(0.2)	(3.5)
Total operating revenues	$ 62.1	$ 81.2	$ 185.5	$ 126.2	$ 60.8	$ 90.8	$ 180.4	$ 133.5	455	465.5	$ 500.7
Spire Alabama | Residential
Disaggregation Of Revenue [Line Items]
Total operating revenues									267.8	265.3
Spire Alabama | Commercial & Industrial
Disaggregation Of Revenue [Line Items]
Total operating revenues									109.4	113.5
Spire Alabama | Transportation
Disaggregation Of Revenue [Line Items]
Total operating revenues									72.9	69.5
Spire Alabama | Off-system & Other Incentive
Disaggregation Of Revenue [Line Items]
Total operating revenues									3.2
Spire Alabama | Other Customer Revenue
Disaggregation Of Revenue [Line Items]
Total operating revenues									$ 1.9	$ 20.7

Revenue - Additional Informatio

Revenue - Additional Information (Details)	12 Months Ended
	Sep. 30, 2020
Revenue Recognition [Line Items]
Remaining performance obligation, practical expedient	true
Maximum
Revenue Recognition [Line Items]
Revenue remaining performance obligation original excepted duration	1 year

Revenue - Schedule of Gross Rec

Revenue - Schedule of Gross Receipts Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Scheduleof Gross Receipts Taxes [Line Items]
Gross receipts taxes recorded in regulated gas distribution operating revenues	$ 91.5	$ 99.3	$ 98.4
Spire Missouri
Scheduleof Gross Receipts Taxes [Line Items]
Gross receipts taxes recorded in regulated gas distribution operating revenues	63.5	71.1	68.9
Spire Alabama
Scheduleof Gross Receipts Taxes [Line Items]
Gross receipts taxes recorded in regulated gas distribution operating revenues	$ 23.3	$ 23.7	$ 25.4

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, minimum	3 years
Number of shares of common stock that may be issued (in shares)	1,000,000
Restricted Stock Awards [Abstract]
Dividend yield percent	0.00%	0.00%	0.00%
Stock Option Awards [Abstract]
Total unrecognized compensation costs	$ 10.8
Weighted average period for recognition of unrecognized compensation costs	1 year 9 months
Restricted Stock Awards
Restricted Stock Awards [Abstract]
Vested restricted stock withheld for tax withholding obligations (in shares)	41,353	28,731	34,922
Vested restricted stock withheld for tax withholding obligations, weighted average price (in dollars per share)	$ 77.07	$ 79.23	$ 81.65
Fair value, restricted stock	$ 9.8	$ 7.6	$ 10.5
Actual tax benefit realized	$ 3.7	$ 2.9	$ 4
Restricted Stock Awards | Performance Vesting
Restricted Stock Awards [Abstract]
Granted (in shares)	91,662
Granted, weighted average grant date fair value (in dollars per share)	$ 76.19
Expiration date	Sep. 30, 2023
Restricted Stock Awards | Time Vesting
Restricted Stock Awards [Abstract]
Granted (in shares)	33,350
Granted, weighted average grant date fair value (in dollars per share)	$ 76.13
Restricted Stock Awards | Executive Officers and Key Employees | Performance Vesting
Restricted Stock Awards [Abstract]
Granted, weighted average grant date fair value (in dollars per share)		$ 80.72	$ 79.88
Maximum amount of shares pursuant to restricted stock awards	200.00%
Number of shares issued for maximum performance payout (in shares)	519,888
Number of shares elected to be defer at target payout (in shares)	59,408	80,760
Restricted Stock Awards | Executive Officers and Key Employees | Time Vesting
Restricted Stock Awards [Abstract]
Granted (in shares)	33,350
Granted, weighted average grant date fair value (in dollars per share)	$ 76.13	$ 76.66	76.60
Restricted Stock Awards | Non Employee Directors | Time Vesting
Restricted Stock Awards [Abstract]
Granted (in shares)	10,560
Granted, weighted average grant date fair value (in dollars per share)	$ 84.58	$ 78.69	$ 63.20

Stock-based Compensation - Rest

Stock-based Compensation - Restricted Stock and Restricted Stock Unit Activity (Details) - Restricted Stock Awards	12 Months Ended
	Sep. 30, 2020$ / sharesshares
Performance Vesting
Shares/ Units
Nonvested at beginning of period (in shares) | shares	263,910
Granted (in shares) | shares	91,662
Vested (in shares) | shares	(86,287)
Forfeited (in shares) | shares	(9,341)
Nonvested at end of period (in shares) | shares	259,944
Weighted Average Grant Date Fair Value Per Share
Nonvested at beginning of period (in dollars per share) | $ / shares	$ 73.20
Granted (in dollars per share) | $ / shares	76.19
Vested (in dollars per share) | $ / shares	58.68
Forfeited (in dollars per share) | $ / shares	79.34
Nonvested at end of period (in dollars per share) | $ / shares	$ 78.92
Time Vesting
Shares/ Units
Nonvested at beginning of period (in shares) | shares	96,277
Granted (in shares) | shares	33,350
Vested (in shares) | shares	(32,326)
Forfeited (in shares) | shares	(3,628)
Nonvested at end of period (in shares) | shares	93,673
Weighted Average Grant Date Fair Value Per Share
Nonvested at beginning of period (in dollars per share) | $ / shares	$ 72.83
Granted (in dollars per share) | $ / shares	76.13
Vested (in dollars per share) | $ / shares	65.28
Forfeited (in dollars per share) | $ / shares	76.94
Nonvested at end of period (in dollars per share) | $ / shares	$ 76.45

Stock-based Compensation - Fair

Stock-based Compensation - Fair Value Measurement Assumptions (Details)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	1.57%	2.88%	1.76%
Expected dividend yield of stock	0.00%	0.00%	0.00%
Expected volatility of stock	16.80%	17.00%	16.00%
Vesting period	3 years	3 years	2 years 10 months 24 days

Stock-based Compensation - Comp

Stock-based Compensation - Compensation Costs Recognized (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Total compensation cost	$ 9.4	$ 8.6	$ 6.9
Compensation cost capitalized	(0.6)	(1.4)	(1.3)
Prior period disallowed stock compensation capitalization	0	0	6.9
Compensation cost recognized in net income	8.8	7.2	12.5
Income tax benefit recognized in net income	(2.1)	(1.7)	(4)
Compensation cost recognized in net income, net of income tax	$ 6.7	$ 5.5	$ 8.5

Earnings Per Common Share - Sch

Earnings Per Common Share - Schedule of Basic and Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Basic Earnings Per Common Share:
Net Income	$ (19.7)	$ (92.3)	$ 133.6	$ 67	$ (34.3)	$ (3)	$ 154.6	$ 67.3	$ 88.6	$ 184.6	$ 214.2
Less: Provision for preferred dividends									14.8	5.3
Income allocated to participating securities									0.1	0.4	0.5
Net Income Available to Common Shareholders									$ 73.7	$ 178.9	$ 213.7
Weighted Average Common Shares Outstanding (in millions)									51.2	50.7	49.1
Basic Earnings Per Share of Common Stock	$ (0.45)	$ (1.87)	$ 2.55	$ 1.24	$ (0.75)	$ (0.09)	$ 3.05	$ 1.33	$ 1.44	$ 3.53	$ 4.35
Diluted Earnings per Common Share:
Net Income	$ (19.7)	$ (92.3)	$ 133.6	$ 67	$ (34.3)	$ (3)	$ 154.6	$ 67.3	$ 88.6	$ 184.6	$ 214.2
Less: Provision for preferred dividends									14.8	5.3
Income allocated to participating securities									0.1	0.4	0.5
Net Income Available to Common Shareholders									$ 73.7	$ 178.9	$ 213.7
Weighted Average Common Shares Outstanding (in millions)									51.2	50.7	49.1
Dilutive Effect of Restricted Stock and Restricted Stock Units (in millions)									0.1	0.1	0.2
Weighted Average Diluted Common Shares (in millions)									51.3	50.8	49.3
Diluted Earnings Per Share of Common Stock	$ (0.45)	$ (1.87)	$ 2.54	$ 1.24	$ (0.74)	$ (0.09)	$ 3.04	$ 1.32	$ 1.44	$ 3.52	$ 4.33

Earnings Per Common Share - S_2

Earnings Per Common Share - Schedule of Basic and Diluted Earnings Per Common Share (Parenthetical) (Details) - shares shares in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Restricted Stock and Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding common shares excluded from calculation of diluted EPS (in shares)	0.1	0.1	0.4

Shareholders' Equity - Addition

Shareholders' Equity - Additional Information (Details) - USD ($)	May 21, 2019	Feb. 06, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Nov. 13, 2020	Mar. 24, 2020
Class Of Stock [Line Items]
Preferred stock shares authorized (in shares)			5,000,000	5,000,000
Percentage of preferred stock	5.90%
Preferred stock, liquidation preference per share	$ 25,000
Net proceeds, after deducting commissions and sale expenses				$ 242,000,000
Preferred stock, redemption date			Aug. 15, 2024
Preferred stock voting rights			Shareholders of the Preferred Stock generally have no voting rights with respect to matters that generally require the approval of voting stockholders. The limited voting rights of holders of the Preferred Stock include the right to vote on certain matters that may affect the preference or special rights of the Preferred Stock. In addition, if and whenever dividends on any shares of Preferred Stock have not been declared and paid for at least six dividend periods, whether or not consecutive, the number of directors then constituting the Board shall automatically be increased by two (to be elected by the holders of the Preferred Stock) until all accumulated and unpaid dividends on the Preferred Stock have been paid in full.
Sale of common stock			$ 32,000,000	14,400,000	$ 153,000,000
Issuance of common stock			$ 41,100,000	19,500,000	$ 154,700,000
SEC effective shelf registration Form S-3 sale and issuance authorization under the dividend reinvestment and stock purchase program (in shares)			250,000
SEC effective shelf registration Form S-3 remaining and available for issuance under the dividend reinvestment and stock purchase program (in shares)			207,254
Dividend payment restriction formula component - fixed amount			$ 8,000,000
Retained earnings available to pay dividends in period			$ 1,269,400,000	$ 1,182,400,000
Spire Missouri
Class Of Stock [Line Items]
Preferred stock shares authorized (in shares)			1,480,000	1,480,000
Preferred stock shares outstanding (in shares)			0	0
Regulatory preferred stock and debt securities issuance, amount authorized			$ 500,000,000
Regulatory preferred stock and debt securities issuance, remaining authorized amount			$ 125,000,000
Preferred stock shares issued (in shares)			0	0
Spire Alabama
Class Of Stock [Line Items]
Preferred stock shares authorized (in shares)			120,000	120,000
Preferred stock shares outstanding (in shares)			0	0
Regulatory preferred stock and debt securities issuance, amount authorized							$ 150,000,000
Preferred stock shares issued (in shares)			0	0
Subsequent Event
Class Of Stock [Line Items]
SEC effective shelf registration Form S-3 remaining and available for issuance under the dividend reinvestment and stock purchase program (in shares)						201,148
ATM Program
Class Of Stock [Line Items]
Sale of common stock		$ 150,000,000
Number of shares issued			446,619	179,630
Issuance of common stock			$ 32,000,000	$ 14,400,000
Redemption prior to August 15, 2024
Class Of Stock [Line Items]
Preferred stock redemption price per share			$ 25,500
Redemption on or after August 15, 2024
Class Of Stock [Line Items]
Preferred stock redemption price per share			$ 25,000
Depositary Shares
Class Of Stock [Line Items]
Preferred stock shares authorized (in shares)			10,000,000	10,000,000
Preferred stock shares outstanding (in shares)	10,000,000		10,000,000	10,000,000
Preferred stock share interest rate	0.10%
Preferred stock, par value	$ 25		$ 25	$ 25
Net proceeds, after deducting commissions and sale expenses	$ 242,000,000
Preferred stock shares issued (in shares)			10,000,000	10,000,000

Shareholders' Equity - Schedule

Shareholders' Equity - Schedule of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
BALANCE		$ 2,543	$ 2,255.4	$ 1,991.3
Other comprehensive (loss) income		(9.9)	(37.7)	2.5
BALANCE		2,522.3	2,543	2,255.4
Spire Missouri
Accumulated Other Comprehensive Income Loss [Line Items]
BALANCE		1,339.3	1,259.9	1,171
Other comprehensive (loss) income		(0.5)	(0.8)	0.4
BALANCE		1,435.1	1,339.3	1,259.9
Net Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income Loss [Line Items]
BALANCE		(29)	7.9
Other comprehensive (loss) income		(9.4)	(36.9)
BALANCE		(38.4)	(29)	7.9
Net Unrealized Gains (Losses) on Cash Flow Hedges | Spire Missouri
Accumulated Other Comprehensive Income Loss [Line Items]
BALANCE		0	0
Other comprehensive (loss) income		0	0
BALANCE		0	0	0
Defined Benefit Pension and Other Postretirement Benefit Plans
Accumulated Other Comprehensive Income Loss [Line Items]
BALANCE		(2.4)	(1.5)
Other comprehensive (loss) income		(0.5)	(0.9)
BALANCE		(2.9)	(2.4)	(1.5)
Defined Benefit Pension and Other Postretirement Benefit Plans | Spire Missouri
Accumulated Other Comprehensive Income Loss [Line Items]
BALANCE		(2.4)	(1.6)
Other comprehensive (loss) income		(0.5)	(0.8)
BALANCE		(2.9)	(2.4)	(1.6)
Net Unrealized Losses on Available-for-Sale Debt Securities
Accumulated Other Comprehensive Income Loss [Line Items]
BALANCE		0.1	0
Other comprehensive (loss) income		0	0.1
BALANCE		0.1	0.1	0
Net Unrealized Losses on Available-for-Sale Debt Securities | Spire Missouri
Accumulated Other Comprehensive Income Loss [Line Items]
BALANCE		0	0
Other comprehensive (loss) income		0	0
BALANCE		0	0	0
AOCI
Accumulated Other Comprehensive Income Loss [Line Items]
BALANCE	[1]	(31.3)	6.4	3.2
Other comprehensive (loss) income	[1]	(9.9)	(37.7)	2.5
BALANCE	[1]	(41.2)	(31.3)	6.4
AOCI | Spire Missouri
Accumulated Other Comprehensive Income Loss [Line Items]
BALANCE	[1]	(2.4)	(1.6)	(1.7)
Other comprehensive (loss) income	[1]	(0.5)	(0.8)	0.4
BALANCE	[1]	$ (2.9)	$ (2.4)	$ (1.6)
[1]	Accumulated other comprehensive income (loss)

Long-term Debt - Schedule of Co

Long-term Debt - Schedule of Composition of Long-term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Long-term Debt
Total principal of long-term debt	$ 2,500	$ 2,137
Less: Unamortized discounts and debt issuance costs	(15.9)	(14.4)
Less: Current portion	(60.4)	(40)
Long-term debt, excluding current portion	2,423.7	2,082.6
Spire Missouri
Long-term Debt
Total principal of long-term debt	1,098	930
Less: Unamortized discounts and debt issuance costs	(6)	(5)
Long-term debt, excluding current portion	1,092	925
Spire Missouri | Floating-rate note due December 1, 2021
Long-term Debt
Total principal of long-term debt		100
Spire Missouri | 3.00% Series, due March 15, 2023
Long-term Debt
Total principal of long-term debt	55	55
Spire Missouri | 3.40% Series, due August 15, 2023
Long-term Debt
Total principal of long-term debt	250	250
Spire Missouri | 3.40% Series, due March 15, 2028
Long-term Debt
Total principal of long-term debt	45	45
Spire Missouri | 7.0% Series, due June 1, 2029
Long-term Debt
Total principal of long-term debt	19.3	25
Spire Missouri | 2.84% Series, due November 15, 2029
Long-term Debt
Total principal of long-term debt	275
Spire Missouri | 7.90% Series, due September 15, 2030
Long-term Debt
Total principal of long-term debt	30	30
Spire Missouri | 3.68% Series, due September 15, 2032
Long-term Debt
Total principal of long-term debt	50	50
Spire Missouri | 6.00% Series, due May 1, 2034
Long-term Debt
Total principal of long-term debt	99.3	100
Spire Missouri | 6.15% Series, due June 1, 2036
Long-term Debt
Total principal of long-term debt	54.5	55
Spire Missouri | 4.63% Series, due August 15, 2043
Long-term Debt
Total principal of long-term debt	99.9	100
Spire Missouri | 4.23% Series, due September 15, 2047
Long-term Debt
Total principal of long-term debt	70	70
Spire Missouri | 4.38% Series, due September 15, 2057
Long-term Debt
Total principal of long-term debt	50	50
Spire Alabama
Long-term Debt
Total principal of long-term debt	475	415
Less: Unamortized discounts and debt issuance costs	(3.2)	(2.8)
Less: Current portion		(40)
Long-term debt, excluding current portion	471.8	372.2
Spire Alabama | 5.20% Notes, due January 15, 2020
Long-term Debt
Total principal of long-term debt		40
Spire Alabama | 3.86% Notes, due December 22, 2021
Long-term Debt
Total principal of long-term debt	50	50
Spire Alabama | 3.21% Notes, due September 15, 2025
Long-term Debt
Total principal of long-term debt	35	35
Spire Alabama | 2.88% Notes, due December 1, 2029
Long-term Debt
Total principal of long-term debt	100
Spire Alabama | 5.90% Notes, due January 15, 2037
Long-term Debt
Total principal of long-term debt	45	45
Spire Alabama | 4.31% Notes, due December 1, 2045
Long-term Debt
Total principal of long-term debt	80	80
Spire Alabama | 3.92% Notes, due January 15, 2048
Long-term Debt
Total principal of long-term debt	45	45
Spire Alabama | 4.64% Notes, due January 15, 2049
Long-term Debt
Total principal of long-term debt	90	90
Spire Alabama | 4.02% Notes, due January 15, 2058
Long-term Debt
Total principal of long-term debt	30	30
Spire | 2.52% Senior Notes, due September 1, 2021
Long-term Debt
Total principal of long-term debt	35	35
Spire | 3.31% Notes Payable, due December 15, 2022
Long-term Debt
Total principal of long-term debt	25	25
Spire | 3.54% Senior Notes, due February 27, 2024
Long-term Debt
Total principal of long-term debt	150	150
Spire | 3.13% Senior Notes, due September 1, 2026
Long-term Debt
Total principal of long-term debt	130	130
Spire | 3.93% Senior Notes, due March 15, 2027
Long-term Debt
Total principal of long-term debt	100	100
Spire | 4.70% Senior Notes, due August 15, 2044
Long-term Debt
Total principal of long-term debt	250	250
Subsidiaries
Long-term Debt
Total principal of long-term debt	237
Subsidiaries | 4.14% First Mortgage Bonds, due September 30, 2021
Long-term Debt
Total principal of long-term debt	20	20
Subsidiaries | 5.00% First Mortgage Bonds, due September 30, 2031
Long-term Debt
Total principal of long-term debt	42	42
Subsidiaries | 2.95% Notes, with Annual Principal Payments through December 2034
Long-term Debt
Total principal of long-term debt	135
Subsidiaries | 3.52% First Mortgage Bonds, due September 30, 2049
Long-term Debt
Total principal of long-term debt	$ 40	$ 40

Long-term Debt - Schedule of _2

Long-term Debt - Schedule of Composition of Long-term Debt (Parenthetical) (Details)	12 Months Ended
	Sep. 30, 2020
Spire Missouri | Floating-rate note due December 1, 2021
Debt Instrument [Line Items]
Debt instrument, maturity date	Dec. 1, 2021
Spire Missouri | 3.00% Series, due March 15, 2023
Debt Instrument [Line Items]
Debt instrument, interest rate	3.00%
Debt instrument, maturity date	Mar. 15, 2023
Spire Missouri | 3.40% Series, due August 15, 2023
Debt Instrument [Line Items]
Debt instrument, interest rate	3.40%
Debt instrument, maturity date	Aug. 15, 2023
Spire Missouri | 3.40% Series, due March 15, 2028
Debt Instrument [Line Items]
Debt instrument, interest rate	3.40%
Debt instrument, maturity date	Mar. 15, 2028
Spire Missouri | 2.84% Series, due November 15, 2029
Debt Instrument [Line Items]
Debt instrument, interest rate	2.84%
Debt instrument, maturity date	Nov. 15, 2029
Spire Missouri | 7.0% Series, due June 1, 2029
Debt Instrument [Line Items]
Debt instrument, interest rate	7.00%
Debt instrument, maturity date	Jun. 1, 2029
Spire Missouri | 7.90% Series, due September 15, 2030
Debt Instrument [Line Items]
Debt instrument, interest rate	7.90%
Debt instrument, maturity date	Sep. 15, 2030
Spire Missouri | 3.68% Series, due September 15, 2032
Debt Instrument [Line Items]
Debt instrument, interest rate	3.68%
Debt instrument, maturity date	Sep. 15, 2032
Spire Missouri | 6.00% Series, due May 1, 2034
Debt Instrument [Line Items]
Debt instrument, interest rate	6.00%
Debt instrument, maturity date	May 1, 2034
Spire Missouri | 6.15% Series, due June 1, 2036
Debt Instrument [Line Items]
Debt instrument, interest rate	6.15%
Debt instrument, maturity date	Jun. 1, 2036
Spire Missouri | 4.63% Series, due August 15, 2043
Debt Instrument [Line Items]
Debt instrument, interest rate	4.63%
Debt instrument, maturity date	Aug. 15, 2043
Spire Missouri | 4.23% Series, due September 15, 2047
Debt Instrument [Line Items]
Debt instrument, interest rate	4.23%
Debt instrument, maturity date	Sep. 15, 2047
Spire Missouri | 4.38% Series, due September 15, 2057
Debt Instrument [Line Items]
Debt instrument, interest rate	4.38%
Debt instrument, maturity date	Sep. 15, 2057
Spire Alabama | 5.20% Notes, due January 15, 2020
Debt Instrument [Line Items]
Debt instrument, interest rate	5.20%
Debt instrument, maturity date	Jan. 15, 2020
Spire Alabama | 3.86% Notes, due December 22, 2021
Debt Instrument [Line Items]
Debt instrument, interest rate	3.86%
Debt instrument, maturity date	Dec. 22, 2021
Spire Alabama | 3.21% Notes, due September 15, 2025
Debt Instrument [Line Items]
Debt instrument, interest rate	3.21%
Debt instrument, maturity date	Sep. 15, 2025
Spire Alabama | 2.88% Notes, due December 1, 2029
Debt Instrument [Line Items]
Debt instrument, interest rate	2.88%
Debt instrument, maturity date	Dec. 1, 2029
Spire Alabama | 5.90% Notes, due January 15, 2037
Debt Instrument [Line Items]
Debt instrument, interest rate	5.90%
Debt instrument, maturity date	Jan. 15, 2037
Spire Alabama | 4.31% Notes, due December 1, 2045
Debt Instrument [Line Items]
Debt instrument, interest rate	4.31%
Debt instrument, maturity date	Dec. 1, 2045
Spire Alabama | 3.92% Notes, due January 15, 2048
Debt Instrument [Line Items]
Debt instrument, interest rate	3.92%
Debt instrument, maturity date	Jan. 15, 2048
Spire Alabama | 4.64% Notes, due January 15, 2049
Debt Instrument [Line Items]
Debt instrument, interest rate	4.64%
Debt instrument, maturity date	Jan. 15, 2049
Spire Alabama | 4.02% Notes, due January 15, 2058
Debt Instrument [Line Items]
Debt instrument, interest rate	4.02%
Debt instrument, maturity date	Jan. 15, 2058
Spire | 2.52% Senior Notes, due September 1, 2021
Debt Instrument [Line Items]
Debt instrument, interest rate	2.52%
Debt instrument, maturity date	Sep. 1, 2021
Spire | 3.31% Notes Payable, due December 15, 2022
Debt Instrument [Line Items]
Debt instrument, interest rate	3.31%
Debt instrument, maturity date	Dec. 15, 2022
Spire | 3.54% Senior Notes, due February 27, 2024
Debt Instrument [Line Items]
Debt instrument, interest rate	3.54%
Debt instrument, maturity date	Feb. 27, 2024
Spire | 3.13% Senior Notes, due September 1, 2026
Debt Instrument [Line Items]
Debt instrument, interest rate	3.13%
Debt instrument, maturity date	Sep. 1, 2026
Spire | 3.93% Senior Notes, due March 15, 2027
Debt Instrument [Line Items]
Debt instrument, interest rate	3.93%
Debt instrument, maturity date	Mar. 15, 2027
Spire | 4.70% Senior Notes, due August 15, 2044
Debt Instrument [Line Items]
Debt instrument, interest rate	4.70%
Debt instrument, maturity date	Aug. 15, 2044
Subsidiaries | 4.14% First Mortgage Bonds, due September 30, 2021
Debt Instrument [Line Items]
Debt instrument, interest rate	4.14%
Debt instrument, maturity date	Sep. 30, 2021
Subsidiaries | 5.00% First Mortgage Bonds, due September 30, 2031
Debt Instrument [Line Items]
Debt instrument, interest rate	5.00%
Debt instrument, maturity date	Sep. 30, 2031
Subsidiaries | 2.95% Notes, with Annual Principal Payments through December 2034
Debt Instrument [Line Items]
Debt instrument, interest rate	2.95%
Debt instrument, maturity date	Dec. 31, 2034
Subsidiaries | 3.52% First Mortgage Bonds, due September 30, 2049
Debt Instrument [Line Items]
Debt instrument, interest rate	3.52%
Debt instrument, maturity date	Sep. 30, 2049

Long-term Debt - Maturities of

Long-term Debt - Maturities of Long-term Debt (Details) $ in Millions	Sep. 30, 2020USD ($)
Maturities on long-term debt [Abstract]
2021	$ 60.4
2022	55.8
2023	336.2
2024	156.6
2025	42
Spire Missouri
Maturities on long-term debt [Abstract]
2021	0
2022	0
2023	305
2024	0
2025	0
Spire Alabama
Maturities on long-term debt [Abstract]
2021	0
2022	50
2023	0
2024	0
2025	$ 35

Long-term Debt - Additional Inf

Long-term Debt - Additional Information (Details) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Mar. 24, 2020
Debt Instrument [Line Items]
Long-term debt	$ 2,500,000,000	$ 2,137,000,000
Interest expense, net	5,800,000	6,800,000	$ 2,600,000
Spire Missouri
Debt Instrument [Line Items]
Long-term debt	1,098,000,000	930,000,000
Interest expense, net	800,000	1,900,000	$ 900,000
Regulatory preferred stock and debt securities issuance, amount authorized	500,000,000
Regulatory preferred stock and debt securities issuance, remaining authorized amount	125,000,000
Spire Alabama
Debt Instrument [Line Items]
Long-term debt	475,000,000	$ 415,000,000
Interest expense, net	1,900,000
Regulatory preferred stock and debt securities issuance, amount authorized				$ 150,000,000
Subsidiaries
Debt Instrument [Line Items]
Long-term debt	$ 237,000,000

Notes Payable and Credit Agre_3

Notes Payable and Credit Agreements - Additional Information (Details)	Mar. 26, 2020USD ($)bank	Sep. 30, 2020USD ($)	Dec. 14, 2016bank
Line of Credit Facility [Line Items]
Long-term debt		$ 975,000,000
Liabilities | Lender Concentration Risk
Line of Credit Facility [Line Items]
Line of credit facility, number of banks in agreement | bank			11
Spire
Line of Credit Facility [Line Items]
Term loan bear interest rate per annum		1.70%
Short-term borrowings used to support lending to Utilities		$ 449,800,000
Spire | Term Loan
Line of Credit Facility [Line Items]
Line of credit facility, number of banks in agreement | bank	2
Long-term debt	$ 150,000,000
Debt instrument, maturity date	Mar. 25, 2021
Team loan interest rate description		The term loan bears interest at the LIBOR Rate (as defined in the loan agreement) plus 0.85% per annum.
Term loan bear interest rate per annum		1.60%
Spire | Term Loan | LIBOR
Line of Credit Facility [Line Items]
Term loan bear interest rate per annum	0.85%
Revolving Credit Facility Borrowings
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity		$ 975,000,000
Minimum required ratio of earnings before interest, taxes, depreciation, and amortization (EBITDA) times interest expense as required by the line of credit covenant		70.00%
Revolving Credit Facility Borrowings | Maximum
Line of Credit Facility [Line Items]
Debt to total capitalization ratio		0.60
Revolving Credit Facility Borrowings | Spire
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity		$ 300,000,000
Term loan bear interest rate per annum		1.90%
Revolving Credit Facility Borrowings | Spire Missouri
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity		$ 475,000,000
Term loan bear interest rate per annum		1.90%
Revolving Credit Facility Borrowings | Spire Alabama
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity		$ 200,000,000
Term loan bear interest rate per annum		1.90%
Commercial Paper Notes
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity		$ 975,000,000
Debt term		365 days
Commercial Paper Notes | Spire
Line of Credit Facility [Line Items]
Term loan bear interest rate per annum		1.70%

Note Payables and Credit Agreem

Note Payables and Credit Agreements - Schedule of Spire Missouri and Alabama Short-term Borrowings (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Spire
Short-term Debt [Line Items]
Weighted average borrowings	$ 576.2
Lowest borrowings outstanding	432.6
Highest borrowings outstanding	$ 856.6
Weighted average interest rate	1.70%
Borrowings outstanding	$ 648	$ 743.2
Weighted average interest rate	0.60%	2.30%
Revolving Credit Facility Borrowings | Spire
Short-term Debt [Line Items]
Weighted average borrowings	$ 0.1
Highest borrowings outstanding	$ 23.1
Weighted average interest rate	1.90%
Commercial Paper Notes | Spire
Short-term Debt [Line Items]
Weighted average borrowings	$ 476.1
Lowest borrowings outstanding	73.5
Highest borrowings outstanding	$ 856.6
Weighted average interest rate	1.70%
Borrowings outstanding	$ 498	$ 743.2
Weighted average interest rate	0.20%	2.30%
Term Loan | Spire
Short-term Debt [Line Items]
Weighted average borrowings	$ 77.5
Highest borrowings outstanding	$ 150
Weighted average interest rate	1.60%
Borrowings outstanding	$ 150
Weighted average interest rate	1.10%
Spire Missouri | Revolving Credit Facility Borrowings
Short-term Debt [Line Items]
Weighted average borrowings	$ 17.9
Highest borrowings outstanding	$ 185.1
Weighted average interest rate	1.90%
Spire Missouri | Spire Note
Short-term Debt [Line Items]
Weighted average borrowings	$ 242
Lowest borrowings outstanding	16
Highest borrowings outstanding	$ 429.5
Weighted average interest rate	1.50%
Borrowings outstanding	$ 301.2	$ 386.4
Weighted average interest rate	0.20%	2.30%
Spire Alabama | Revolving Credit Facility Borrowings
Short-term Debt [Line Items]
Weighted average borrowings	$ 4.6
Highest borrowings outstanding	$ 50
Weighted average interest rate	1.90%
Spire Alabama | Spire Note
Short-term Debt [Line Items]
Weighted average borrowings	$ 89
Lowest borrowings outstanding	18.5
Highest borrowings outstanding	$ 161.3
Weighted average interest rate	1.40%
Borrowings outstanding	$ 121.3	$ 128.7
Weighted average interest rate	0.20%	2.30%

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Summary of Financial Instruments Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Quoted Prices in Active Markets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 4.1	$ 5.8
Quoted Prices in Active Markets (Level 1) | Spire Missouri
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents		2.6
Significant Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable	648	743.2
Long-term debt, including current portion	2,908.6	2,373.4
Significant Observable Inputs (Level 2) | Spire Missouri
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable	301.2	386.4
Long-term debt, including current portion	1,313.5	1,065.2
Significant Observable Inputs (Level 2) | Spire Alabama
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable	121.3	128.7
Long-term debt, including current portion	576.9	474.8
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	4.1	5.8
Notes payable	648	743.2
Long-term debt, including current portion	2,484.1	2,122.6
Carrying Amount | Spire Missouri
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents		2.6
Notes payable	301.2	386.4
Long-term debt, including current portion	1,092	925
Carrying Amount | Spire Alabama
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable	121.3	128.7
Long-term debt, including current portion	471.8	412.2
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	4.1	5.8
Notes payable	648	743.2
Long-term debt, including current portion	2,908.6	2,373.4
Fair Value | Spire Missouri
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents		2.6
Notes payable	301.2	386.4
Long-term debt, including current portion	1,313.5	1,065.2
Fair Value | Spire Alabama
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable	121.3	128.7
Long-term debt, including current portion	$ 576.9	$ 474.8

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
ASSETS
Derivative asset after the effects of netting	$ 17.2	$ 14.8
LIABILITIES
Derivative liability after the effects of netting	76.5	54.8
Spire Missouri
ASSETS
Derivative asset after the effects of netting	0	0
LIABILITIES
Derivative liability after the effects of netting	0	0
Fair Value, Measurements, Recurring
ASSETS
Effects of netting and cash margin receivables/payables	(32)	(9.4)
Derivative asset after the effects of netting	57.7	50.8
LIABILITIES
Effects of netting and cash margin receivables/payables	(23)	(23.7)
Derivative liability after the effects of netting	76.5	54.8
Fair Value, Measurements, Recurring | Spire Missouri
ASSETS
Effects of netting and cash margin receivables/payables	(6.6)
Derivative asset after the effects of netting	21.9
Fair Value, Measurements, Recurring | U.S. stock/bond mutual funds | Spire Missouri
ASSETS
Effects of netting and cash margin receivables/payables	0	0
Derivative asset after the effects of netting	21.9	20.5
Fair Value, Measurements, Recurring | Gasoline and heating oil contracts | Spire Missouri
ASSETS
Effects of netting and cash margin receivables/payables	(0.3)
Derivative asset after the effects of netting	0
Fair Value, Measurements, Recurring | NYMEX/ICE natural gas contracts | Spire Missouri
ASSETS
Effects of netting and cash margin receivables/payables	(6.3)
Derivative asset after the effects of netting	0
LIABILITIES
Effects of netting and cash margin receivables/payables	(0.9)	(12.3)
Derivative liability after the effects of netting	0	0
Fair Value, Measurements, Recurring | Other | U.S. stock/bond mutual funds
ASSETS
Effects of netting and cash margin receivables/payables	0	0
Derivative asset after the effects of netting	18.6	15.5
Fair Value, Measurements, Recurring | Other | Interest Rate Swap
LIABILITIES
Effects of netting and cash margin receivables/payables	0	0
Derivative liability after the effects of netting	54.2	43.4
Fair Value, Measurements, Recurring | Gas Utility | Operating Segments | U.S. stock/bond mutual funds
ASSETS
Effects of netting and cash margin receivables/payables	0	0
Derivative asset after the effects of netting	21.9	20.5
Fair Value, Measurements, Recurring | Gas Utility | Operating Segments | Gasoline and heating oil contracts
ASSETS
Effects of netting and cash margin receivables/payables	(0.3)
Derivative asset after the effects of netting	0
Fair Value, Measurements, Recurring | Gas Utility | Operating Segments | NYMEX/ICE natural gas contracts
ASSETS
Effects of netting and cash margin receivables/payables	(6.3)
Derivative asset after the effects of netting	0
LIABILITIES
Effects of netting and cash margin receivables/payables	(0.9)	(12.3)
Derivative liability after the effects of netting	0	0
Fair Value, Measurements, Recurring | Gas Marketing | Operating Segments | NYMEX/ICE natural gas contracts
ASSETS
Effects of netting and cash margin receivables/payables	(25.4)	(6.9)
Derivative asset after the effects of netting	2.3	0.5
LIABILITIES
Effects of netting and cash margin receivables/payables	(22.1)	(8.9)
Derivative liability after the effects of netting	0	0
Fair Value, Measurements, Recurring | Gas Marketing | Operating Segments | Natural gas commodity contracts
ASSETS
Effects of netting and cash margin receivables/payables	0	(2.5)
Derivative asset after the effects of netting	14.9	14.3
LIABILITIES
Effects of netting and cash margin receivables/payables	0	(2.5)
Derivative liability after the effects of netting	22.3	11.4
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1)
ASSETS
Derivative asset before effects of netting	47.1	36.9
LIABILITIES
Derivative liability before effects of netting	1.6	12.7
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Spire Missouri
ASSETS
Derivative asset before effects of netting	28.5
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | U.S. stock/bond mutual funds | Spire Missouri
ASSETS
Derivative asset before effects of netting	21.9	20.5
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Gasoline and heating oil contracts | Spire Missouri
ASSETS
Derivative asset before effects of netting	0.3
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | NYMEX/ICE natural gas contracts | Spire Missouri
ASSETS
Derivative asset before effects of netting	6.3
LIABILITIES
Derivative liability before effects of netting	0.9	12.3
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Other | U.S. stock/bond mutual funds
ASSETS
Derivative asset before effects of netting	18.6	15.5
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Other | Interest Rate Swap
LIABILITIES
Derivative liability before effects of netting	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Gas Utility | Operating Segments | U.S. stock/bond mutual funds
ASSETS
Derivative asset before effects of netting	21.9	20.5
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Gas Utility | Operating Segments | Gasoline and heating oil contracts
ASSETS
Derivative asset before effects of netting	0.3
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Gas Utility | Operating Segments | NYMEX/ICE natural gas contracts
ASSETS
Derivative asset before effects of netting	6.3
LIABILITIES
Derivative liability before effects of netting	0.9	12.3
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Gas Marketing | Operating Segments | NYMEX/ICE natural gas contracts
ASSETS
Derivative asset before effects of netting	0	0.9
LIABILITIES
Derivative liability before effects of netting	0.7	0.4
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1) | Gas Marketing | Operating Segments | Natural gas commodity contracts
ASSETS
Derivative asset before effects of netting	0	0
LIABILITIES
Derivative liability before effects of netting	0	0
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level 2)
ASSETS
Derivative asset before effects of netting	42.2	23.3
LIABILITIES
Derivative liability before effects of netting	97.9	65.7
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level 2) | Spire Missouri
ASSETS
Derivative asset before effects of netting	0
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level 2) | U.S. stock/bond mutual funds | Spire Missouri
ASSETS
Derivative asset before effects of netting	0	0
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level 2) | Gasoline and heating oil contracts | Spire Missouri
ASSETS
Derivative asset before effects of netting	0
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level 2) | NYMEX/ICE natural gas contracts | Spire Missouri
ASSETS
Derivative asset before effects of netting	0
LIABILITIES
Derivative liability before effects of netting	0	0
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level 2) | Other | U.S. stock/bond mutual funds
ASSETS
Derivative asset before effects of netting	0	0
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level 2) | Other | Interest Rate Swap
LIABILITIES
Derivative liability before effects of netting	54.2	43.4
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level 2) | Gas Utility | Operating Segments | U.S. stock/bond mutual funds
ASSETS
Derivative asset before effects of netting	0	0
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level 2) | Gas Utility | Operating Segments | Gasoline and heating oil contracts
ASSETS
Derivative asset before effects of netting	0
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level 2) | Gas Utility | Operating Segments | NYMEX/ICE natural gas contracts
ASSETS
Derivative asset before effects of netting	0
LIABILITIES
Derivative liability before effects of netting	0	0
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level 2) | Gas Marketing | Operating Segments | NYMEX/ICE natural gas contracts
ASSETS
Derivative asset before effects of netting	27.7	6.5
LIABILITIES
Derivative liability before effects of netting	21.4	8.5
Fair Value, Measurements, Recurring | Significant Observable Inputs (Level 2) | Gas Marketing | Operating Segments | Natural gas commodity contracts
ASSETS
Derivative asset before effects of netting	14.5	16.8
LIABILITIES
Derivative liability before effects of netting	22.3	13.8
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
ASSETS
Derivative asset before effects of netting	0.4	0
LIABILITIES
Derivative liability before effects of netting	0	0.1
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Spire Missouri
ASSETS
Derivative asset before effects of netting	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | U.S. stock/bond mutual funds | Spire Missouri
ASSETS
Derivative asset before effects of netting	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Gasoline and heating oil contracts | Spire Missouri
ASSETS
Derivative asset before effects of netting	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | NYMEX/ICE natural gas contracts | Spire Missouri
ASSETS
Derivative asset before effects of netting	0
LIABILITIES
Derivative liability before effects of netting	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Other | U.S. stock/bond mutual funds
ASSETS
Derivative asset before effects of netting	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Other | Interest Rate Swap
LIABILITIES
Derivative liability before effects of netting	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Gas Utility | Operating Segments | U.S. stock/bond mutual funds
ASSETS
Derivative asset before effects of netting	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Gas Utility | Operating Segments | Gasoline and heating oil contracts
ASSETS
Derivative asset before effects of netting	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Gas Utility | Operating Segments | NYMEX/ICE natural gas contracts
ASSETS
Derivative asset before effects of netting	0
LIABILITIES
Derivative liability before effects of netting	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Gas Marketing | Operating Segments | NYMEX/ICE natural gas contracts
ASSETS
Derivative asset before effects of netting	0	0
LIABILITIES
Derivative liability before effects of netting	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Gas Marketing | Operating Segments | Natural gas commodity contracts
ASSETS
Derivative asset before effects of netting	0.4	0
LIABILITIES
Derivative liability before effects of netting	$ 0	$ 0.1

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	Sep. 30, 2020	Sep. 30, 2019
Spire Alabama
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Outstanding derivative contracts	$ 0	$ 0

Derivative Instruments and He_3

Derivative Instruments and Hedging Activities - Additional Information (Details) MMBTU in Millions, $ in Millions	1 Months Ended	3 Months Ended				12 Months Ended
	Aug. 31, 2018USD ($)	Sep. 30, 2020USD ($)MMBTU	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2020USD ($)MMBTU	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)
Derivative [Line Items]
Notional amount of non-exchange traded natural gas commodity contracts (in MMBtu) | MMBTU		278.3				278.3
Notional amount of non-exchange traded natural gas commodity contracts to be settled during fiscal 2021 (in MMBtu) | MMBTU		233.1				233.1
Notional amount of non-exchange traded natural gas commodity contracts to be settled during fiscal 2022 (in MMBtu) | MMBTU		35.7				35.7
Notional amount of non-exchange traded natural gas commodity to be settled during fiscal 2023 (in MMBtu) | MMBTU		5.8				5.8
Notional amount of non-exchange traded natural gas commodity to be settled during fiscal 2024 (in MMBtu) | MMBTU		1.3				1.3
Notional amount of non-exchange traded natural gas commodity to be settled during fiscal 2025 (in MMBtu) | MMBTU		1.6				1.6
Notional amount of non-exchange traded natural gas commodity to be settled during fiscal 2026 (in MMBtu) | MMBTU		0.8				0.8
Loss on termination and settlement of interest rate swap		$ 0.3
Cash margin receivables not offset with derivatives		7.6				$ 7.6	$ 8.1
Spire Missouri
Derivative [Line Items]
Cash margin receivables not offset with derivatives							$ 7.2	$ 7.8
Interest Rate Swap with Fixed Interest Rate of 2.7675%
Derivative [Line Items]
Derivative, term of contract	3 years
Derivative fixed interest rate	2.7675%
Notional amount	$ 100
Loss on termination and settlement of interest rate swap				$ 2.5
Interest Rate Swap with Fixed Interest Rate of 3.250%
Derivative [Line Items]
Derivative, term of contract					3 years
Derivative fixed interest rate					3.25%
Notional amount					$ 100
Cumulative mark-to-market loss in accumulated other comprehensive loss		$ (53.7)				(53.7)
Interest Rate Swap with Fixed Interest Rate of 0.921% to 1.3105%
Derivative [Line Items]
Notional amount				$ 150
Mark-to-market loss						$ (0.5)
Interest Rate Swap with Fixed Interest Rate of 0.761%
Derivative [Line Items]
Derivative, term of contract			10 years
Derivative fixed interest rate			0.761%
Notional amount			$ 40
Minimum [Member] | Interest Rate Swap with Fixed Interest Rate of 0.921% to 1.3105%
Derivative [Line Items]
Derivative fixed interest rate				0.921%
Maximum | Interest Rate Swap with Fixed Interest Rate of 0.921% to 1.3105%
Derivative [Line Items]
Derivative fixed interest rate				1.3105%

Derivative Instruments and He_4

Derivative Instruments and Hedging Activities - Exchange-Traded/Cleared Derivatives (Details) - MMBTU MMBTU in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Natural Gas Futures Purchased | Gas Marketing
Derivative [Line Items]
Notional (MMBtu millions)	22.9	29.1
Maximum Term (Months)	41 months	36 months
Natural Gas Futures Purchased | Gas Utility
Derivative [Line Items]
Notional (MMBtu millions)	25.9	69
Maximum Term (Months)	12 months	12 months
Natural Gas Options Purchased Net | Gas Marketing
Derivative [Line Items]
Notional (MMBtu millions)	4.8	6.9
Maximum Term (Months)	6 months	12 months
Natural Gas Basis Swaps Purchased | Gas Marketing
Derivative [Line Items]
Notional (MMBtu millions)	6.2	90.1
Maximum Term (Months)	24 months	36 months

Derivative Instruments and He_5

Derivative Instruments and Hedging Activities - Effect of Derivative Instruments on Statements of Consolidated Income and Statements of Consolidated Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Derivatives in Cash Flow Hedging Relationships [Abstract]
Net hedging gain (loss) arising during the period	$ (8.9)	$ (46.4)	$ 3.9
Derivatives in Cash Flow Hedging Relationships | Cash Flow Hedging
Derivatives in Cash Flow Hedging Relationships [Abstract]
Effective portion of gain (loss) reclassified from AOCI to income	(3.2)	1.3	1.5
Derivatives in Cash Flow Hedging Relationships | Cash Flow Hedging | Other Comprehensive Income (Loss)
Derivatives in Cash Flow Hedging Relationships [Abstract]
Net hedging gain (loss) arising during the period	(8.9)	(46.4)	3.9
Derivatives in Cash Flow Hedging Relationships | Cash Flow Hedging | Interest rate swaps | Other Comprehensive Income (Loss)
Derivatives in Cash Flow Hedging Relationships [Abstract]
Net hedging gain (loss) arising during the period	(8.9)	(46.4)	3.9
Derivatives in Cash Flow Hedging Relationships | Cash Flow Hedging | Interest rate swaps | Interest Expense
Derivatives in Cash Flow Hedging Relationships [Abstract]
Effective portion of gain (loss) reclassified from AOCI to income	(3.2)	1.3	1.4
Derivatives in Cash Flow Hedging Relationships | Cash Flow Hedging | Gasoline and Heating Oil Contracts | Gas Utility Other Operating Expenses
Derivatives in Cash Flow Hedging Relationships [Abstract]
Effective portion of gain (loss) reclassified from AOCI to income	0	0	0.1
Not Designated as Hedging Instrument
Derivatives Not Designated as Hedging Instruments [Abstract]
Gain (loss) recognized in income on derivatives	(2.6)	(5.9)	2.1
Not Designated as Hedging Instrument | Natural gas commodity contracts | Non Regulated Gas Marketing Operating Revenue
Derivatives Not Designated as Hedging Instruments [Abstract]
Gain (loss) recognized in income on derivatives	9.2	2.5	10.2
Not Designated as Hedging Instrument | Natural gas commodity contracts | Non Regulated Gas Marketing Operating Expenses
Derivatives Not Designated as Hedging Instruments [Abstract]
Gain (loss) recognized in income on derivatives	0	(8.4)	(8.1)
Not Designated as Hedging Instrument | NYMEX / ICE Natural Gas Contracts | Non Regulated Gas Marketing Operating Revenue
Derivatives Not Designated as Hedging Instruments [Abstract]
Gain (loss) recognized in income on derivatives	$ (11.8)	$ 0	$ 0

Derivative Instruments and He_6

Derivative Instruments and Hedging Activities - Fair Value of Derivative Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Derivatives, Fair Value [Line Items]
Fair value of derivative assets presented above	$ 49.2	$ 24.2
Fair value of derivative liabilities presented above	99.5	78.5
Derivatives in Cash Flow Hedging Relationships
Derivatives, Fair Value [Line Items]
Fair value of derivative assets presented above	0	0
Fair value of derivative liabilities presented above	54.2	43.4
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair value of derivative assets presented above	49.2	24.2
Fair value of derivative liabilities presented above	45.3	35.1
Gasoline and Heating Oil Contracts | Not Designated as Hedging Instrument | Derivative Instruments Assets
Derivatives, Fair Value [Line Items]
Fair value of derivative assets presented above	0.3
Fair value of derivative liabilities presented above	0
Other | Interest rate swaps | Derivatives in Cash Flow Hedging Relationships | Derivative Instrument Liability
Derivatives, Fair Value [Line Items]
Fair value of derivative assets presented above	0
Fair value of derivative liabilities presented above	54.2
Other | Interest rate swaps | Derivatives in Cash Flow Hedging Relationships | Derivative Instruments Assets
Derivatives, Fair Value [Line Items]
Fair value of derivative assets presented above		0
Fair value of derivative liabilities presented above		43.4
Gas Utility | Operating Segments | Natural Gas Contracts | Not Designated as Hedging Instrument | Accounts Receivable – Other
Derivatives, Fair Value [Line Items]
Fair value of derivative assets presented above	6.3	0
Fair value of derivative liabilities presented above	0.9	12.3
Gas Marketing | Operating Segments | NYMEX / ICE natural gas contracts | Not Designated as Hedging Instrument | Derivative Instruments Assets
Derivatives, Fair Value [Line Items]
Fair value of derivative assets presented above	20.5	7
Fair value of derivative liabilities presented above	21.3	7.3
Gas Marketing | Operating Segments | NYMEX / ICE natural gas contracts | Not Designated as Hedging Instrument | Deferred Charges – Other
Derivatives, Fair Value [Line Items]
Fair value of derivative assets presented above	7.2	0.5
Fair value of derivative liabilities presented above	0.8	1.6
Gas Marketing | Operating Segments | Natural gas commodity contracts | Not Designated as Hedging Instrument | Derivative Instruments Assets
Derivatives, Fair Value [Line Items]
Fair value of derivative assets presented above	13.5	10.4
Fair value of derivative liabilities presented above	0	0.9
Gas Marketing | Operating Segments | Natural gas commodity contracts | Not Designated as Hedging Instrument | Deferred Charges – Other
Derivatives, Fair Value [Line Items]
Fair value of derivative assets presented above	1.4	4.8
Fair value of derivative liabilities presented above	0	0
Gas Marketing | Operating Segments | Natural gas commodity contracts | Not Designated as Hedging Instrument | Current Liabilities – Other
Derivatives, Fair Value [Line Items]
Fair value of derivative assets presented above	0	1.4
Fair value of derivative liabilities presented above	16.8	11.5
Gas Marketing | Operating Segments | Natural gas commodity contracts | Not Designated as Hedging Instrument | Deferred Credits – Other
Derivatives, Fair Value [Line Items]
Fair value of derivative assets presented above	0	0.1
Fair value of derivative liabilities presented above	$ 5.5	$ 1.5

Derivative Instruments and He_7

Derivative Instruments and Hedging Activities - Derivative Instruments Reconciliation (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Offsetting Derivative Assets [Abstract]
Fair value of derivative assets presented above	$ 49.2	$ 24.2
Fair value of cash margin receivable offset with derivatives	(9)	14.3
Netting of assets and liabilities with the same counterparty	(23)	(23.7)
Derivative asset after the effects of netting	17.2	14.8
Current Assets – Other	15.8	4.2
Deferred Charges and Other Assets – Other	1.4	10.6
Offsetting Derivative Liabilities [Abstract]
Fair value of derivative liabilities presented above	99.5	78.5
Netting of assets and liabilities with the same counterparty	(23)	(23.7)
Derivative liability after the effects of netting	76.5	54.8
Current Liabilities – Other	71	50
Deferred Credits and Other Liabilities – Other	$ 5.5	$ 4.8

Derivative Instruments and He_8

Derivative Instruments and Hedging Activities - Open NYMEX Natural Gas Futures Positions (Details) - Spire Missouri - Natural Gas Futures Purchased MMBTU in Millions	12 Months Ended
	Sep. 30, 2020MMBTU
Derivative [Line Items]
Notional (MMBtu millions)	25.9
Maximum Term (Months)	12 months

Derivative Instruments and He_9

Derivative Instruments and Hedging Activities - Effect of Derivative Instruments on the Statement of Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Derivative [Line Items]
Net hedging gain (loss) arising during the period	$ (8.9)	$ (46.4)	$ 3.9
Cash Flow Hedging | Derivatives in Cash Flow Hedging Relationships
Derivative [Line Items]
Effective portion of gain (loss) reclassified from AOCI to income	(3.2)	1.3	1.5
Cash Flow Hedging | Derivatives in Cash Flow Hedging Relationships | Other Comprehensive Income (Loss)
Derivative [Line Items]
Net hedging gain (loss) arising during the period	(8.9)	(46.4)	3.9
Cash Flow Hedging | Derivatives in Cash Flow Hedging Relationships | Gas Utility Other Operating Expenses | Gasoline and Heating Oil Contracts
Derivative [Line Items]
Effective portion of gain (loss) reclassified from AOCI to income	0	0	0.1
Spire Missouri | Cash Flow Hedging | Derivatives in Cash Flow Hedging Relationships | Other Comprehensive Income (Loss) | Gasoline and Heating Oil Contracts
Derivative [Line Items]
Net hedging gain (loss) arising during the period	0	0	0
Spire Missouri | Cash Flow Hedging | Derivatives in Cash Flow Hedging Relationships | Gas Utility Other Operating Expenses | Gasoline and Heating Oil Contracts
Derivative [Line Items]
Effective portion of gain (loss) reclassified from AOCI to income	$ 0	$ 0	$ 0.1

Derivative Instruments and H_10

Derivative Instruments and Hedging Activities - Fair Value of Derivative Instruments in the Balance Sheets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Derivative [Line Items]
Fair value of derivative assets presented above	$ 49.2	$ 24.2
Fair value of derivative liabilities presented above	99.5	78.5
Not Designated as Hedging Instrument
Derivative [Line Items]
Fair value of derivative assets presented above	49.2	24.2
Fair value of derivative liabilities presented above	45.3	35.1
Not Designated as Hedging Instrument | Derivative Instruments Assets | Gasoline and Heating Oil Contracts
Derivative [Line Items]
Fair value of derivative assets presented above	0.3
Fair value of derivative liabilities presented above	0
Spire Missouri
Derivative [Line Items]
Fair value of derivative assets presented above	6.6	0
Fair value of derivative liabilities presented above	0.9	12.3
Spire Missouri | Not Designated as Hedging Instrument
Derivative [Line Items]
Fair value of derivative assets presented above	6.6
Fair value of derivative liabilities presented above	0.9
Spire Missouri | Not Designated as Hedging Instrument | Accounts Receivable – Other | Gas Utility | Natural Gas Contracts
Derivative [Line Items]
Fair value of derivative assets presented above	6.3	0
Fair value of derivative liabilities presented above	0.9	$ 12.3
Spire Missouri | Not Designated as Hedging Instrument | Derivative Instruments Assets | Gas Utility | Gasoline and Heating Oil Contracts
Derivative [Line Items]
Fair value of derivative assets presented above	0.3
Fair value of derivative liabilities presented above	$ 0

Derivative Instruments and H_11

Derivative Instruments and Hedging Activities - Reconciliation to Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Derivative [Line Items]
Fair value of derivative assets presented above	$ 49.2	$ 24.2
Netting of assets and liabilities with the same counterparty	(23)	(23.7)
Derivative asset after the effects of netting	17.2	14.8
Fair value of derivative liabilities presented above	99.5	78.5
Netting of assets and liabilities with the same counterparty	(23)	(23.7)
Derivative liability after the effects of netting	76.5	54.8
Spire Missouri
Derivative [Line Items]
Fair value of derivative assets presented above	6.6	0
Fair value of cash margin (payable) receivable offset with derivatives	(5.7)	12.3
Netting of assets and liabilities with the same counterparty	(0.9)	(12.3)
Derivative asset after the effects of netting	0	0
Fair value of derivative liabilities presented above	0.9	12.3
Netting of assets and liabilities with the same counterparty	(0.9)	(12.3)
Derivative liability after the effects of netting	$ 0	$ 0

Concentrations of Credit Risk -

Concentrations of Credit Risk - Additional Information (Details) customer in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)customerStatecounterparty
Concentration Risk [Line Items]
Number of large counterparties for which credit risk is disclosed | counterparty	5
Number of counterparties with investment-grade rating | counterparty	4
Utility Companies And Their Marketing Affiliates
Concentration Risk [Line Items]
Accounts receivable | $	$ 73
Five Largest Counterparties
Concentration Risk [Line Items]
Accounts receivable | $	$ 35.7
Gas Utility
Concentration Risk [Line Items]
Number of customer serves | customer	1.7
Number of state serves across multiple rate classes | State	3

Income Taxes - Net Provisions f

Income Taxes - Net Provisions for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
State and local:
Total income tax expense (benefit)	$ 12.4	$ 34.5	$ (26.5)
Spire
Federal:
Current	0.4	0.6	0
Deferred	5.8	27.4	(22.7)
Investment tax credits	(0.2)	(0.2)	(0.2)
State and local:
Current	3	2.1	2.2
Deferred	3.4	4.6	(5.8)
Total income tax expense (benefit)	12.4	34.5	(26.5)
Spire Missouri
Federal:
Current	0	0	0
Deferred	14.9	11.5	(26.1)
Investment tax credits	(0.2)	(0.2)	(0.2)
State and local:
Current	0.1	0	0
Deferred	2.5	2	(6.3)
Total income tax expense (benefit)	17.3	13.3	(32.6)
Spire Alabama
Federal:
Current	0	0	0
Deferred	17.4	16.3	81.5
Investment tax credits	0	0	0
State and local:
Current	0	0	0
Deferred	4.6	4.2	0.1
Total income tax expense (benefit)	$ 22	$ 20.5	$ 81.6

Income Taxes - Effective Income

Income Taxes - Effective Income Tax Rate Variation from Stated Tax Rate (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Contingency [Line Items]
Federal income tax statutory rate	35.00%	21.00%
Spire
Income Tax Contingency [Line Items]
Federal income tax statutory rate		21.00%	21.00%	24.50%
State and local income taxes, net of federal income tax benefits		9.00%	3.60%	3.40%
Certain expenses capitalized on books and deducted on tax return		(6.60%)	(3.80%)	(2.30%)
Taxes related to prior years		(1.80%)	0.20%	(0.40%)
Tax law changes		0.00%	0.00%	(35.90%)
Amortization of excess deferred taxes		(8.30%)	(3.80%)	(1.80%)
Other items – net		(1.00%)	(1.40%)	(1.60%)
Effective income tax rate		12.30%	15.80%	(14.10%)
Spire Missouri
Income Tax Contingency [Line Items]
Federal income tax statutory rate		21.00%	21.00%	24.50%
State and local income taxes, net of federal income tax benefits		2.60%	2.60%	3.40%
Certain expenses capitalized on books and deducted on tax return		(4.60%)	(6.50%)	(4.60%)
Taxes related to prior years		(1.40%)	0.10%	(0.70%)
Tax law changes		0.00%	0.00%	(50.30%)
Amortization of excess deferred taxes		(5.70%)	(6.60%)	(3.60%)
Other items – net		(0.20%)	(0.30%)	(2.50%)
Effective income tax rate		11.70%	10.30%	(33.80%)
Spire Alabama
Income Tax Contingency [Line Items]
Federal income tax statutory rate		21.00%	21.00%	24.50%
State and local income taxes, net of federal income tax benefits		4.10%	4.10%	3.80%
Certain expenses capitalized on books and deducted on tax return		0.00%	0.00%	0.00%
Taxes related to prior years		0.10%	0.00%	0.00%
Tax law changes		0.00%	0.00%	70.00%
Amortization of excess deferred taxes		0.00%	0.00%	0.00%
Other items – net		(0.10%)	0.20%	0.10%
Effective income tax rate		25.10%	25.30%	98.40%

Income Taxes - Significant Item

Income Taxes - Significant Items in Net Deferred Tax Liability (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Spire
Deferred tax assets:
Reserves not currently deductible	$ 24.8	$ 31.4
Pension and other postretirement benefits	108.3	102.7
Goodwill	0	0
Operating losses	170.4	162.2
Regulatory amount due to customers, net	36.1	46.5
Other	44.7	20
Deferred tax assets	384.3	362.8
Less: Valuation allowance	(0.9)	(1.8)
Total deferred tax assets	383.4	361
Deferred tax liabilities:
Relating to property	(614)	(562.9)
Regulatory pension and other postretirement benefits	(138.4)	(135.9)
Other	(142.4)	(113.6)
Total deferred tax liabilities	(894.8)	(812.4)
Net deferred tax (liability)	(511.4)	(451.4)
Spire Missouri
Deferred tax assets:
Reserves not currently deductible	16.7	21.2
Pension and other postretirement benefits	78.5	78.7
Goodwill	0	0
Operating losses	36	51.1
Regulatory amount due to customers, net	32.3	42.7
Other	0	1.2
Deferred tax assets	163.5	194.9
Less: Valuation allowance	(0.9)	(1.8)
Total deferred tax assets	162.6	193.1
Deferred tax liabilities:
Relating to property	(427.1)	(395.1)
Regulatory pension and other postretirement benefits	(107.4)	(111.7)
Other	(62.8)	(50.9)
Total deferred tax liabilities	(597.3)	(557.7)
Net deferred tax (liability)	(434.7)	(364.6)
Spire Alabama
Deferred tax assets:
Reserves not currently deductible	5.9	6.2
Pension and other postretirement benefits	0	0
Goodwill	101.3	116.8
Operating losses	111.3	94.2
Regulatory amount due to customers, net	0	0
Other	0	0
Deferred tax assets	218.5	217.2
Less: Valuation allowance	0	0
Total deferred tax assets	218.5	217.2
Deferred tax liabilities:
Relating to property	(151.4)	(129.3)
Regulatory pension and other postretirement benefits	(3.4)	(2)
Other	(4.4)	(4.6)
Total deferred tax liabilities	(159.2)	(135.9)
Net deferred tax asset	$ 59.3	$ 81.3

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Tax Credit Carryforward [Line Items]
Federal income tax statutory rate	35.00%	21.00%
Unrecognized tax benefits affect on the Company's effective tax rate		$ 2,900,000	$ 2,500,000
Income tax penalties accrued		0	0
Income taxes accrued		$ 0	$ 0
Spire
Tax Credit Carryforward [Line Items]
Federal income tax statutory rate		21.00%	21.00%	24.50%
Federal and state loss carryforwards		$ 726,800,000
Contribution carryforwards		9,300,000
Valuation allowance		3,600,000
Tax credit carryforwards		2,900,000
Tax credit carryforwards, valuation allowance		$ 100,000
Tax credit carryforwards, expiration year		2020
Spire | State
Tax Credit Carryforward [Line Items]
Operating loss carryforwards, expiration year		2030
Spire | Federal and Other States
Tax Credit Carryforward [Line Items]
Operating loss carryforwards, expiration year		2035
Spire Missouri
Tax Credit Carryforward [Line Items]
Federal income tax statutory rate		21.00%	21.00%	24.50%
Excess accumulated deferred taxes		$ 8,400,000	$ 8,400,000
Federal and state loss carryforwards		207,800,000
Contribution carryforwards		5,400,000
Valuation allowance		3,000,000
Tax credit carryforwards		2,000,000
Tax credit carryforwards, valuation allowance		$ 100,000
Tax credit carryforwards, expiration year		2020
Unrecognized tax benefits affect on the Company's effective tax rate		$ 2,700,000	$ 2,200,000
Spire Missouri | State
Tax Credit Carryforward [Line Items]
Operating loss carryforwards, expiration year		2035
Spire Missouri | Federal
Tax Credit Carryforward [Line Items]
Operating loss carryforwards, expiration year		2035
Spire Alabama
Tax Credit Carryforward [Line Items]
Federal income tax statutory rate		21.00%	21.00%	24.50%
Federal and state loss carryforwards		$ 443,500,000
Unrecognized tax benefits affect on the Company's effective tax rate		$ 0	$ 0	$ 0
Spire Alabama | State
Tax Credit Carryforward [Line Items]
Operating loss carryforwards, expiration year		2030
Spire Alabama | Federal
Tax Credit Carryforward [Line Items]
Operating loss carryforwards, expiration year		2035

Income Taxes - Impact of Tax Cu

Income Taxes - Impact of Tax Cuts and Jobs Act (Details) $ in Millions	12 Months Ended
	Sep. 30, 2018USD ($)
Spire
Deferred Income Tax Assets And Liabilities [Line Items]
Adjustment to deferred tax liabilities	$ (318.3)
Adjustment to deferred income tax expense	(75)
Adjustment to regulatory assets	(75.9)
Adjustment to regulatory liabilities	167.4
Spire Missouri
Deferred Income Tax Assets And Liabilities [Line Items]
Adjustment to deferred tax liabilities	(285.3)
Adjustment to deferred income tax expense	(57)
Adjustment to regulatory assets	(78.1)
Adjustment to regulatory liabilities	150.2
Spire Alabama
Deferred Income Tax Assets And Liabilities [Line Items]
Adjustment to deferred tax liabilities	(61)
Adjustment to deferred income tax expense	58.8
Adjustment to regulatory assets	$ 2.2

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefit Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Spire
Unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits, beginning of year	$ 10.7	$ 8.1	$ 11
Decrease related to tax law changes	0	0	(4)
Increases related to tax positions taken in current year	2.6	4.5	1.2
Reductions related to tax positions taken in prior year	0	(1.9)	0
Reductions due to lapse of applicable statute of limitations	(0.1)	0	(0.1)
Unrecognized tax benefits, end of year	13.2	10.7	8.1
Spire Missouri
Unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits, beginning of year	10.4	7.8	10.7
Decrease related to tax law changes	0	0	(4)
Increases related to tax positions taken in current year	2.6	4.5	1.1
Reductions related to tax positions taken in prior year	0	(1.9)	0
Reductions due to lapse of applicable statute of limitations	0	0	0
Unrecognized tax benefits, end of year	$ 13	$ 10.4	$ 7.8

Pension Plans and Other Postr_3

Pension Plans and Other Postretirement Benefits - Schedule of Net Periodic Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Pension Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost – benefits earned during the period	$ 22.5	$ 19.3	$ 20.2
Interest cost on projected benefit obligation	22.6	28.2	27.4
Expected return on plan assets	(35)	(36.3)	(37)
Amortization of prior service (credit) cost	(2.5)	(1.1)	(0.9)
Amortization of actuarial (gain) loss	14.4	9.3	10.9
Loss on lump-sum settlements and curtailments	31.6	0	18.6
Subtotal	53.6	19.4	39.2
Regulatory adjustment	6.6	39.6	37.4
Net pension cost	60.2	59	76.6
Other Postretirement Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost – benefits earned during the period	5.9	7.4	9.4
Interest cost on projected benefit obligation	6.3	9	8.6
Expected return on plan assets	(16.7)	(16.2)	(13.9)
Amortization of prior service (credit) cost	(0.5)	(0.1)	(0.1)
Amortization of actuarial (gain) loss	(2)	(0.5)	0.8
Subtotal	(7)	(0.4)	4.8
Regulatory adjustment	16	10	2.2
Net pension cost	9	9.6	7
Spire Missouri | Pension Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost – benefits earned during the period	15.7	12.4	12.7
Interest cost on projected benefit obligation	15.8	19.8	19.5
Expected return on plan assets	(24.6)	(25.5)	(27.2)
Amortization of prior service (credit) cost	0.1	0.9	0.9
Amortization of actuarial (gain) loss	11.3	8.7	9.4
Loss on lump-sum settlements and curtailments	26.6	0	16.1
Subtotal	44.9	16.3	31.4
Regulatory adjustment	3.9	31.8	32.1
Net pension cost	48.8	48.1	63.5
Spire Missouri | Other Postretirement Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost – benefits earned during the period	5.3	6.8	9
Interest cost on projected benefit obligation	4.7	6.9	6.9
Expected return on plan assets	(11.4)	(11.1)	(9.6)
Amortization of prior service (credit) cost	(0.2)	0.3	0.3
Amortization of actuarial (gain) loss	(2)	(0.5)	0.9
Subtotal	(3.6)	2.4	7.5
Regulatory adjustment	17.7	11.7	3.9
Net pension cost	14.1	14.1	11.4
Spire Alabama | Pension Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost – benefits earned during the period	6.1	6.2	6.4
Interest cost on projected benefit obligation	4.9	6	5.5
Expected return on plan assets	(6.9)	(7.3)	(6.5)
Amortization of prior service (credit) cost	(2.4)	(1.8)	(1.8)
Amortization of actuarial (gain) loss	3.1	0.8	1.5
Loss on lump-sum settlements and curtailments	5	0	2.4
Subtotal	9.8	3.9	7.5
Regulatory adjustment	1.8	6.9	4.5
Net pension cost	11.6	10.8	12
Spire Alabama | Other Postretirement Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost – benefits earned during the period	0.4	0.4	0.2
Interest cost on projected benefit obligation	1.4	1.8	1.5
Expected return on plan assets	(5)	(4.8)	(4.1)
Amortization of prior service (credit) cost	(0.3)	(0.4)	(0.4)
Amortization of actuarial (gain) loss	0	0	(0.1)
Subtotal	(3.5)	(3)	(2.9)
Regulatory adjustment	(1.8)	(1.8)	(1.8)
Net pension cost	$ (5.3)	$ (4.8)	$ (4.7)

Pension Plans and Other Postr_4

Pension Plans and Other Postretirement Benefits - Schedule of Changes in Plan Assets and Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Amortization of actuarial gain (loss)	$ (0.5)	$ (0.9)	$ 0.4
Pension Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial loss (gain)	68	90.9	(1.4)
Amortization of actuarial gain (loss)	(14.4)	(9.3)	(10.9)
Acceleration of loss recognized due to settlement	(31.7)	0	(18.5)
Current year service credit	(4.4)	(10.2)	(0.1)
Transfer due to merger	0	0	0.1
Amortization of prior service credit (cost)	2.5	1.1	(2.9)
Amortization of transition asset	0	0	1.8
Subtotal	20	72.5	(31.9)
Regulatory adjustment	(19.5)	(71.7)	31.6
Total recognized in OCI	0.5	0.8	(0.3)
Other Postretirement Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial loss (gain)	(7.3)	(12.2)	(45.1)
Amortization of actuarial gain (loss)	2	0.5	(0.8)
Current year prior service credit (cost)	15.8	5.5	0
Amortization of current year service cost	0	0.4	0
Amortization of prior service credit (cost)	0.5	(0.3)	0.1
Subtotal	11	(6.1)	(45.8)
Regulatory adjustment	(11)	6.1	45.8
Total recognized in OCI	0	0	0
Spire Missouri | Pension Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial loss (gain)	37.8	59	2.2
Amortization of actuarial gain (loss)	(11.3)	(8.7)	(9.4)
Acceleration of loss recognized due to settlement	(26.6)	0	(16.1)
Current year service credit	(4.4)	(3.7)	0
Transfer due to merger	0	0	0.1
Amortization of prior service credit (cost)	(0.1)	(0.9)	(0.9)
Amortization of transition asset	0	0	0
Subtotal	(4.6)	45.7	(24.1)
Regulatory adjustment	5.1	(44.9)	23.8
Total recognized in OCI	0.5	0.8	(0.3)
Spire Missouri | Other Postretirement Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial loss (gain)	(7.6)	(17.3)	(47.1)
Amortization of actuarial gain (loss)	2	0.5	(0.9)
Current year prior service credit (cost)	9.5	4.9	0
Amortization of current year service cost	0	0	0
Amortization of prior service credit (cost)	0.2	(0.3)	(0.3)
Subtotal	4.1	(12.2)	(48.3)
Regulatory adjustment	(4.1)	12.2	48.3
Total recognized in OCI	0	0	0
Spire Alabama | Pension Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial loss (gain)	24.4	26.3	(0.6)
Amortization of actuarial gain (loss)	(3.1)	(0.8)	(1.5)
Acceleration of loss recognized due to settlement	(5.1)	0	(2.4)
Current year service credit	0	(6.5)	0
Transfer due to merger	0	0	0
Amortization of prior service credit (cost)	2.4	1.8	0
Amortization of transition asset	0	0	1.8
Subtotal	18.6	20.8	(2.7)
Regulatory adjustment	(18.6)	(20.8)	2.7
Total recognized in OCI	0	0	0
Spire Alabama | Other Postretirement Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial loss (gain)	1.1	5.5	1.6
Amortization of actuarial gain (loss)	0	0	0.1
Current year prior service credit (cost)	6.3	0.6	0
Amortization of current year service cost	0	0.4	0
Amortization of prior service credit (cost)	0.3	0	0.4
Subtotal	7.7	6.5	2.1
Regulatory adjustment	(7.7)	(6.5)	(2.1)
Total recognized in OCI	$ 0	$ 0	$ 0

Pension Plans and Other Postr_5

Pension Plans and Other Postretirement Benefits - Additional Information (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)plan	Sep. 30, 2019USD ($)plan	Sep. 30, 2018USD ($)	Apr. 19, 2018USD ($)	Apr. 18, 2018USD ($)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Implementation period used to calculate return on plan assets	4 years
Gains or losses includible in cost amortized to extent exceeds benefit obligations or market-related value of plan assets, percentage	10.00%
Regulatory assets	$ 1,138.9	$ 846.2
Remaining recovery period for regulatory assets for which no return on investment during recovery period is provided	15 years
Medical insurance available until age is reached after early retirement	65 years
Recovery in rates for postretirement benefit					$ 8.6
401(K) plans, cost of defined contributions	$ 13.6	13.8	$ 12.5
Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory assets	580.8	536.9
401(K) plans, cost of defined contributions	9.5	10	9
Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory assets	510.3	265.1
401(K) plans, cost of defined contributions	3.4	$ 3.1	$ 3
Spire Missouri West | Pension Cost | MoPSC | Infrastructure System Replacement Surcharge
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory assets				$ 5.5	9.9
Spire Missouri West | Pension and Other Postretirement Benefits
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Amortization of assets	$ 26.2
Spire Missouri East | Pension Cost | MoPSC | Infrastructure System Replacement Surcharge
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory assets				$ 29	$ 15.5
Spire Missouri East | Pension and Other Postretirement Benefits
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Remaining recovery period for regulatory assets for which no return on investment during recovery period is provided	8 years
Amortization of assets	$ 173
Pension Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rates	3.00%	3.00%
Settlement benefits paid	$ 89.3
Employer contributions	$ 43.7	$ 27.8
Pension Plans | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rates	2.85%	3.20%
Settlement benefits paid	$ 74.5
Number Of Plans | plan	2
Anticipated Contributions to pension plans for qualified trust	$ 36.4
Anticipated contributions to pension plans for non-qualified plans	0.6
Employer contributions	$ 30.3	$ 27.1
Pension Plans | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rates	2.95%	3.20%
Settlement benefits paid	$ 14.8
Number Of Plans | plan	1	0
Anticipated Contributions to pension plans for qualified trust	$ 11.3
Employer contributions	12.7	$ 0.5
Other Postretirement Benefits Plan
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer contributions	0.2	0.6
Anticipated contributions to the postretirement plans for qualified trusts	4.8
Anticipated payment directly to participants in postretirement plan	0.6
Other Postretirement Benefits Plan | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer contributions	$ 0.2	$ 0.6
Other Postretirement Benefits Plan | Spire Missouri East
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rates	3.00%	3.00%

Pension Plans and Other Postr_6

Pension Plans and Other Postretirement Benefits - Reconciliation of the Beginning and Ending Balances of Benefit Obligation (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Pension Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, beginning of year	$ 751.4	$ 664.6
Service cost	22.5	19.3	$ 20.2
Interest cost	22.6	28.2	27.4
Actuarial loss (gain)	37.5	104.8
Plan amendments	(4.4)	(10.2)
Settlement loss	16.5
Settlement benefits paid	(89.3)
Regular benefits paid	(24.2)	(55.3)
Benefit obligation, end of year	732.6	751.4	664.6
Accumulated benefit obligation, end of year	699.3	712.9
Pension Plans | Spire Missouri
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, beginning of year	538.4	473.3
Service cost	15.7	12.4	12.7
Interest cost	15.8	19.8	19.5
Actuarial loss (gain)	15.6	76
Plan amendments	(4.4)	(3.7)
Settlement loss	16.5
Settlement benefits paid	(74.5)
Regular benefits paid	(17.9)	(39.4)
Benefit obligation, end of year	505.2	538.4	473.3
Accumulated benefit obligation, end of year	473.7	500.2
Pension Plans | Spire Alabama
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, beginning of year	152.5	136.3
Service cost	6.1	6.2	6.4
Interest cost	4.9	6	5.5
Actuarial loss (gain)	18.4	23.7
Plan amendments		(6.5)
Settlement benefits paid	(14.8)
Regular benefits paid	(3.6)	(13.2)
Benefit obligation, end of year	163.5	152.5	136.3
Accumulated benefit obligation, end of year	161.8	152.3
Other Postretirement Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, beginning of year	197.3	208.1
Service cost	5.9	7.4	9.4
Interest cost	6.3	9	8.6
Actuarial loss (gain)	0.2	(18.9)
Plan amendments	15.8	5.5
Retiree drug subsidy program		0.2
Regular benefits paid	(13.2)	(14)
Benefit obligation, end of year	212.3	197.3	208.1
Other Postretirement Plans | Spire Missouri
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, beginning of year	147.9	158.8
Service cost	5.3	6.8	9
Interest cost	4.7	6.9	6.9
Actuarial loss (gain)	1.7	(19.5)
Plan amendments	9.5	4.9
Retiree drug subsidy program		0.2
Regular benefits paid	(10.7)	(10.2)
Benefit obligation, end of year	158.4	147.9	158.8
Other Postretirement Plans | Spire Alabama
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, beginning of year	43.4	43.1
Service cost	0.4	0.4	0.2
Interest cost	1.4	1.8	1.5
Actuarial loss (gain)	(0.7)	1.2
Plan amendments	6.3	0.6
Regular benefits paid	(2.5)	(3.7)
Benefit obligation, end of year	$ 48.3	$ 43.4	$ 43.1

Pension Plans and Other Postr_7

Pension Plans and Other Postretirement Benefits - Fair Value of Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Pension Plans
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of year	$ 521.8	$ 499.2
Actual return on plan assets	21.1	50.1
Employer contributions	43.7	27.8
Settlement benefits paid	(89.3)
Regular benefits paid	(24.2)	(55.3)
Fair value of plan assets, end of year	473.1	521.8
Funded status of plans, end of year	(259.5)	(229.6)
Pension Plans | Spire Missouri
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of year	379.2	349.1
Actual return on plan assets	19.1	42.4
Employer contributions	30.3	27.1
Settlement benefits paid	(74.5)
Regular benefits paid	(17.9)	(39.4)
Fair value of plan assets, end of year	336.2	379.2
Funded status of plans, end of year	(169)	(159.2)
Pension Plans | Spire Alabama
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of year	93.3	101.3
Actual return on plan assets	1	4.7
Employer contributions	12.7	0.5
Settlement benefits paid	(14.8)
Regular benefits paid	(3.6)	(13.2)
Fair value of plan assets, end of year	88.6	93.3
Funded status of plans, end of year	(74.9)	(59.2)
Other Postretirement Plans
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of year	279.8	283.5
Actual return on plan assets	24.2	9.7
Employer contributions	0.2	0.6
Regular benefits paid	(13.2)	(14)
Fair value of plan assets, end of year	291	279.8
Funded status of plans, end of year	78.7	82.5
Other Postretirement Plans | Spire Missouri
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of year	188.9	189.5
Actual return on plan assets	20.8	9
Employer contributions	0.2	0.6
Regular benefits paid	(10.7)	(10.2)
Fair value of plan assets, end of year	199.2	188.9
Funded status of plans, end of year	40.8	41
Other Postretirement Plans | Spire Alabama
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of year	86.4	89.6
Actual return on plan assets	3.1	0.5
Regular benefits paid	(2.5)	(3.7)
Fair value of plan assets, end of year	87	86.4
Funded status of plans, end of year	$ 38.7	$ 43

Pension Plans and Other Postr_8

Pension Plans and Other Postretirement Benefits - Amounts Recognized in Balance Sheets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Noncurrent liabilities	$ (309)	$ (264.8)
Spire Missouri
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Noncurrent liabilities	(217.2)	(192.4)
Spire Alabama
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Noncurrent liabilities	(74.9)	(59.2)
Pension Plans
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Current liabilities	(0.6)	(0.5)
Noncurrent liabilities	(258.9)	(229.1)
Total	(259.5)	(229.6)
Pension Plans | Spire Missouri
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Current liabilities	(0.6)	(0.5)
Noncurrent liabilities	(168.4)	(158.7)
Total	(169)	(159.2)
Pension Plans | Spire Alabama
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Current liabilities	0	0
Noncurrent liabilities	(74.9)	(59.2)
Total	(74.9)	(59.2)
Other Postretirement Plans
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Noncurrent assets	129	118.3
Current liabilities	(0.5)	(0.5)
Noncurrent liabilities	(49.8)	(35.3)
Total	78.7	82.5
Other Postretirement Plans | Spire Missouri
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Noncurrent assets	90.3	75.3
Current liabilities	(0.5)	(0.5)
Noncurrent liabilities	(49)	(33.8)
Total	40.8	41
Other Postretirement Plans | Spire Alabama
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract]
Noncurrent assets	38.7	43
Current liabilities	0	0
Noncurrent liabilities	0	0
Total	$ 38.7	$ 43

Pension Plans and Other Postr_9

Pension Plans and Other Postretirement Benefits - Pre-tax Amounts Recognized in Accumulated Other Comprehensive Loss Not Yet Recognized as Components of Net Periodic Pension Costs (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Pension Plans
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of:
Net actuarial loss	$ 235.6	$ 213.7
Prior service (credit) cost	(25.6)	(23.7)
Subtotal	210	190
Adjustments for amounts included in regulatory assets	(206.7)	(187.1)
Total	3.3	2.9
Other Postretirement Plans
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of:
Net actuarial loss	(61.7)	(56.3)
Prior service (credit) cost	15.5	(1)
Subtotal	(46.2)	(57.3)
Adjustments for amounts included in regulatory assets	46.2	57.3
Spire Missouri | Pension Plans
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of:
Net actuarial loss	152.9	153.1
Prior service (credit) cost	(2.8)	1.7
Subtotal	150.1	154.8
Adjustments for amounts included in regulatory assets	(146.8)	(151.9)
Total	3.3	2.9
Spire Missouri | Other Postretirement Plans
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of:
Net actuarial loss	(58.3)	(52.6)
Prior service (credit) cost	10.4	0.6
Subtotal	(47.9)	(52)
Adjustments for amounts included in regulatory assets	47.9	52
Spire Alabama | Pension Plans
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of:
Net actuarial loss	78.1	61.9
Prior service (credit) cost	(21.1)	(23.5)
Subtotal	57	38.4
Adjustments for amounts included in regulatory assets	(57)	(38.4)
Total	0	0
Spire Alabama | Other Postretirement Plans
Pre-tax amounts recognized in accumulated other comprehensive income not yet recognized as components of net periodic pension cost consist of:
Net actuarial loss	(1.5)	(2.6)
Prior service (credit) cost	5.1	(1.6)
Subtotal	3.6	(4.2)
Adjustments for amounts included in regulatory assets	$ (3.6)	$ 4.2

Pension Plans and Other Post_10

Pension Plans and Other Postretirement Benefits - Pre-tax Amounts Expected to Amortized From Accumulated Other Comprehensive Loss Into Net Periodic Pension Cost (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)
Pension Plans
Pre-tax amounts are expected to be amortized from accumulated other comprehensive income [Abstract]
Amortization of net actuarial (gain) loss	$ 16
Amortization of prior service (credit) cost	(3.2)
Subtotal	12.8
Regulatory adjustment	(12.5)
Total	0.3
Pension Plans | Spire Missouri
Pre-tax amounts are expected to be amortized from accumulated other comprehensive income [Abstract]
Amortization of net actuarial (gain) loss	11.4
Amortization of prior service (credit) cost	(0.6)
Subtotal	10.8
Regulatory adjustment	(10.5)
Total	0.3
Pension Plans | Spire Alabama
Pre-tax amounts are expected to be amortized from accumulated other comprehensive income [Abstract]
Amortization of net actuarial (gain) loss	4.6
Amortization of prior service (credit) cost	(2.4)
Subtotal	2.2
Regulatory adjustment	(2.2)
Total	0
Other Postretirement Plans
Pre-tax amounts are expected to be amortized from accumulated other comprehensive income [Abstract]
Amortization of net actuarial (gain) loss	(1.6)
Amortization of prior service (credit) cost	1
Subtotal	(0.6)
Regulatory adjustment	0.6
Other Postretirement Plans | Spire Missouri
Pre-tax amounts are expected to be amortized from accumulated other comprehensive income [Abstract]
Amortization of net actuarial (gain) loss	(1.5)
Amortization of prior service (credit) cost	0.7
Subtotal	(0.8)
Regulatory adjustment	0.8
Other Postretirement Plans | Spire Alabama
Pre-tax amounts are expected to be amortized from accumulated other comprehensive income [Abstract]
Amortization of prior service (credit) cost	0.3
Subtotal	0.3
Regulatory adjustment	$ (0.3)

Pension Plans and Other Post_11

Pension Plans and Other Postretirement Benefits - Assumptions Used to Calculate Net Periodic Cost and Benefit Obligations (Details)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Pension Plans
Assumptions used to calculate benefit obligations [Abstract]
Discount rates	3.00%	3.00%
Pension Plans | Spire Missouri East
Assumptions used to calculate net periodic cost [Abstract]
Weighted average discount rate	3.20%	4.30%	3.75%
Assumptions used to calculate benefit obligations [Abstract]
Weighted average discount rate	2.85%	3.20%
Pension Plans | Spire Missouri West
Assumptions used to calculate net periodic cost [Abstract]
Weighted average discount rate	3.15%	4.35%	3.70%
Assumptions used to calculate benefit obligations [Abstract]
Weighted average discount rate	2.75%	3.15%
Pension Plans | Spire Missouri
Assumptions used to calculate net periodic cost [Abstract]
Weighted average rate of future compensation increase	3.00%	3.00%	3.00%
Expected long-term rate of return on plan assets	7.25%	7.50%	7.75%
Assumptions used to calculate benefit obligations [Abstract]
Discount rates	2.85%	3.20%
Expected long-term rate of return on plan assets	7.25%	7.50%	7.75%
Pension Plans | Spire Alabama
Assumptions used to calculate net periodic cost [Abstract]
Weighted average discount rate		4.35%
Weighted average rate of future compensation increase	3.00%	3.00%	3.00%
Expected long-term rate of return on plan assets	7.25%	7.25%	7.25%
Assumptions used to calculate benefit obligations [Abstract]
Discount rates	2.95%	3.20%
Expected long-term rate of return on plan assets	7.25%	7.25%	7.25%
Pension Plans | Spire Alabama | Maximum
Assumptions used to calculate net periodic cost [Abstract]
Weighted average discount rate	3.25%		3.70%
Assumptions used to calculate benefit obligations [Abstract]
Weighted average discount rate	2.95%	3.25%
Pension Plans | Spire Alabama | Minimum [Member]
Assumptions used to calculate net periodic cost [Abstract]
Weighted average discount rate	3.20%		3.65%
Assumptions used to calculate benefit obligations [Abstract]
Weighted average discount rate	2.80%	3.20%
Other Postretirement Plans | Spire Missouri East
Assumptions used to calculate benefit obligations [Abstract]
Discount rates	3.00%	3.00%
Other Postretirement Plans | Spire Missouri
Assumptions used to calculate net periodic cost [Abstract]
Weighted average discount rate	3.15%	4.30%	3.60%
Weighted average rate of future compensation increase	3.00%	3.00%	3.00%
Expected long-term rate of return on plan assets	6.25%	6.25%
Assumptions used to calculate benefit obligations [Abstract]
Weighted average discount rate	2.75%	3.15%
Expected long-term rate of return on plan assets	6.25%	6.25%
Other Postretirement Plans | Spire Missouri | Maximum
Assumptions used to calculate net periodic cost [Abstract]
Expected long-term rate of return on plan assets			7.75%
Assumptions used to calculate benefit obligations [Abstract]
Expected long-term rate of return on plan assets			7.75%
Other Postretirement Plans | Spire Missouri | Minimum [Member]
Assumptions used to calculate net periodic cost [Abstract]
Expected long-term rate of return on plan assets			5.75%
Assumptions used to calculate benefit obligations [Abstract]
Expected long-term rate of return on plan assets			5.75%
Other Postretirement Plans | Spire Alabama
Assumptions used to calculate net periodic cost [Abstract]
Weighted average discount rate	3.15%	4.30%	3.80%
Assumptions used to calculate benefit obligations [Abstract]
Weighted average discount rate	2.75%	3.15%
Other Postretirement Plans | Spire Alabama | Maximum
Assumptions used to calculate net periodic cost [Abstract]
Expected long-term rate of return on plan assets	6.25%	6.25%	6.00%
Assumptions used to calculate benefit obligations [Abstract]
Expected long-term rate of return on plan assets	6.25%	6.25%	6.00%
Other Postretirement Plans | Spire Alabama | Minimum [Member]
Assumptions used to calculate net periodic cost [Abstract]
Expected long-term rate of return on plan assets	5.00%	5.00%	3.75%
Assumptions used to calculate benefit obligations [Abstract]
Expected long-term rate of return on plan assets	5.00%	5.00%	3.75%

Pension Plans and Other Post_12

Pension Plans and Other Postretirement Benefits - Schedule of Projected Benefit Obligation, Accumulated Benefit Obligation, and Fair Value of Plan Assets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 732.6	$ 751.4
Accumulated benefit obligation	699.3	712.9
Fair value of plan assets	473.1	521.8
Spire Missouri
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	505.2	538.4
Accumulated benefit obligation	473.7	500.2
Fair value of plan assets	336.2	379.2
Spire Alabama
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	163.5	152.5
Accumulated benefit obligation	161.8	152.3
Fair value of plan assets	$ 88.6	$ 93.3

Pension Plans and Other Post_13

Pension Plans and Other Postretirement Benefits - Schedule of Targeted and Actual Plan Assets by Category (Details)	Sep. 30, 2020	Sep. 30, 2019
Spire Missouri | Pension Plans
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	100.00%	100.00%
Actual allocation of plan assets	100.00%	100.00%
Spire Missouri | Pension Plans | Return Seeking Assets
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	70.00%	56.50%
Actual allocation of plan assets	70.00%	57.00%
Spire Missouri | Pension Plans | Liability Hedging Assets
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	30.00%	43.50%
Actual allocation of plan assets	27.00%	39.80%
Spire Missouri | Pension Plans | Other
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	0.00%	0.00%
Actual allocation of plan assets	3.00%	3.20%
Spire Missouri | Other Postretirement Plans
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	100.00%
Actual allocation of plan assets	100.00%	100.00%
Spire Missouri | Other Postretirement Plans | Other
Targeted and actual plan assets by category [Abstract]
Actual allocation of plan assets	4.80%	2.80%
Spire Missouri | Other Postretirement Plans | Equity markets
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	60.00%
Actual allocation of plan assets	57.40%	58.40%
Spire Missouri | Other Postretirement Plans | Debt securities
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	40.00%
Actual allocation of plan assets	37.80%	38.80%
Spire Alabama | Pension Plans
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	100.00%	100.00%
Actual allocation of plan assets	100.00%	100.00%
Spire Alabama | Pension Plans | Return Seeking Assets
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	70.00%	60.00%
Actual allocation of plan assets	71.00%	58.50%
Spire Alabama | Pension Plans | Liability Hedging Assets
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	30.00%	29.00%
Actual allocation of plan assets	27.00%	29.80%
Spire Alabama | Pension Plans | Other
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	0.00%	11.00%
Actual allocation of plan assets	2.00%	11.70%
Spire Alabama | Other Postretirement Plans
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	100.00%
Actual allocation of plan assets	100.00%	100.00%
Spire Alabama | Other Postretirement Plans | Equity markets
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	60.00%
Actual allocation of plan assets	61.80%	60.30%
Spire Alabama | Other Postretirement Plans | Debt securities
Targeted and actual plan assets by category [Abstract]
Targeted allocation of plan assets	40.00%
Actual allocation of plan assets	38.20%	39.70%

Pension Plans and Other Post_14

Pension Plans and Other Postretirement Benefits - Expected Future Benefit Payments (Details) $ in Millions	Sep. 30, 2020USD ($)
Pension Plans
Expected benefit payments [Abstract]
2021	$ 65.6
2022	64.1
2023	60.8
2024	58.6
2025	54.4
2026- 2030	246
Pension Plans | Spire Missouri
Expected benefit payments [Abstract]
2021	49.1
2022	45.6
2023	43.3
2024	41.9
2025	37.7
2026- 2030	168.7
Pension Plans | Spire Alabama
Expected benefit payments [Abstract]
2021	13.5
2022	15.4
2023	14.3
2024	13.5
2025	13.3
2026- 2030	59
Other Postretirement Plans
Expected benefit payments [Abstract]
2021	14.7
2022	15.4
2023	16.1
2024	16.5
2025	16.6
2026- 2030	78.2
Other Postretirement Plans | Spire Missouri
Expected benefit payments [Abstract]
2021	11.7
2022	12.3
2023	12.9
2024	13.2
2025	13.3
2026- 2030	61.7
Other Postretirement Plans | Spire Alabama
Expected benefit payments [Abstract]
2021	2.7
2022	2.8
2023	2.9
2024	3
2025	3
2026- 2030	$ 14.2

Pension Plans and Other Post_15

Pension Plans and Other Postretirement Benefits - Assumed Medical Cost Trend Rates and Effect of 1% Changed (Details) - Other Postretirement Plans - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Rate to which the medical cost trend rate is assumed to decline (the ultimate medical cost trend rate)	5.00%	5.00%
Year the rate reaches the ultimate trend	2025	2025
Assumed 1% change in the assumed medical cost trend rate [Abstract]
Effect of 1% increase on net periodic postretirement benefit cost	$ 0.8
Effect of 1% increase on accumulated postretirement benefit obligation	9.7
Effect of 1% decrease on net periodic postretirement benefit cost	(0.7)
Effect of 1% decrease on accumulated postretirement benefit obligation	$ (8.7)
Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Medical cost trend assumed for next year	6.50%	6.75%
Assumed 1% change in the assumed medical cost trend rate [Abstract]
Effect of 1% increase on net periodic postretirement benefit cost	$ 0.6
Effect of 1% increase on accumulated postretirement benefit obligation	6.5
Effect of 1% decrease on net periodic postretirement benefit cost	(0.6)
Effect of 1% decrease on accumulated postretirement benefit obligation	$ (5.9)
Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Medical cost trend assumed for next year	6.50%	6.75%
Assumed 1% change in the assumed medical cost trend rate [Abstract]
Effect of 1% increase on net periodic postretirement benefit cost	$ 0.2
Effect of 1% increase on accumulated postretirement benefit obligation	2.6
Effect of 1% decrease on net periodic postretirement benefit cost	(0.1)
Effect of 1% decrease on accumulated postretirement benefit obligation	$ (2.3)

Pension Plans and Other Post_16

Pension Plans and Other Postretirement Benefits - Fair Value Measurements of Plan Assets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Pension Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	$ 473.1	$ 521.8	$ 499.2
Pension Plans | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	336.2	379.2	349.1
Pension Plans | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	88.6	93.3	101.3
Pension Plans | Cash and cash equivalents
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	11.5	42.5
Pension Plans | Cash and cash equivalents | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	9.5	41.2
Pension Plans | Cash and cash equivalents | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0.9	0.8
Pension Plans | Equity funds - global (including U.S.)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	227
Pension Plans | Equity funds - global (including U.S.) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	159.9
Pension Plans | Equity funds - global (including U.S.) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	43.6
Pension Plans | Equity index funds - global (including U.S.)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	32.6
Pension Plans | Equity index funds - global (including U.S.) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	22.8
Pension Plans | Equity index funds - global (including U.S.) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	6.4
Pension Plans | Equity mutual funds - U.S.
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		57.5
Pension Plans | Equity mutual funds - U.S. | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		9.1
Pension Plans | Equity mutual funds - U.S. | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		31.7
Pension Plans | Equity mutual funds - international
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		38.7
Pension Plans | Equity mutual funds - international | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		3.3
Pension Plans | Equity mutual funds - international | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		23.2
Pension Plans | U.S. bond funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	48.9
Pension Plans | U.S. bond funds | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	31
Pension Plans | U.S. bond funds | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	11.7
Pension Plans | U.S. government index funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	78.3
Pension Plans | U.S. government index funds | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	59.6
Pension Plans | U.S. government index funds | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	12.1
Pension Plans | Global funds (including U.S.)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	74.8
Pension Plans | Global funds (including U.S.) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	53.4
Pension Plans | Global funds (including U.S.) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	13.9
Pension Plans | Derivatives and margin receivable
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0.2
Pension Plans | Derivatives and margin receivable | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0.2
Pension Plans | U.S. bond mutual funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		108.7
Pension Plans | U.S. bond mutual funds | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		73.9
Pension Plans | U.S. bond mutual funds | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		22.8
Pension Plans | U.S. government
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		62.4
Pension Plans | U.S. government | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		59.7
Pension Plans | U.S. government | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		1.7
Pension Plans | U.S. corporate
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		143.7
Pension Plans | U.S. corporate | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		143.7
Pension Plans | U.S. municipal
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		4
Pension Plans | U.S. municipal | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		4
Pension Plans | International
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		51.6
Pension Plans | International | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		44.1
Pension Plans | International | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		4.9
Pension Plans | 103-12 Direct Filing Entities
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		12.5
Pension Plans | 103-12 Direct Filing Entities | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		8.2
Pension Plans | Quoted Prices in Active Markets (Level 1)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	202.7	392.8
Pension Plans | Quoted Prices in Active Markets (Level 1) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	145	286.1
Pension Plans | Quoted Prices in Active Markets (Level 1) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	37.2	69.8
Pension Plans | Quoted Prices in Active Markets (Level 1) | Cash and cash equivalents
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	11.5	42.5
Pension Plans | Quoted Prices in Active Markets (Level 1) | Cash and cash equivalents | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	9.5	41.2
Pension Plans | Quoted Prices in Active Markets (Level 1) | Cash and cash equivalents | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0.9	0.8
Pension Plans | Quoted Prices in Active Markets (Level 1) | Equity funds - global (including U.S.)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	31.4
Pension Plans | Quoted Prices in Active Markets (Level 1) | Equity funds - global (including U.S.) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	22.1
Pension Plans | Quoted Prices in Active Markets (Level 1) | Equity funds - global (including U.S.) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	6.1
Pension Plans | Quoted Prices in Active Markets (Level 1) | Equity index funds - global (including U.S.)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	32.6
Pension Plans | Quoted Prices in Active Markets (Level 1) | Equity index funds - global (including U.S.) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	22.8
Pension Plans | Quoted Prices in Active Markets (Level 1) | Equity index funds - global (including U.S.) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	6.4
Pension Plans | Quoted Prices in Active Markets (Level 1) | Equity mutual funds - U.S.
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		40.5
Pension Plans | Quoted Prices in Active Markets (Level 1) | Equity mutual funds - U.S. | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Quoted Prices in Active Markets (Level 1) | Equity mutual funds - U.S. | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		26.5
Pension Plans | Quoted Prices in Active Markets (Level 1) | Equity mutual funds - international
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		30.1
Pension Plans | Quoted Prices in Active Markets (Level 1) | Equity mutual funds - international | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Quoted Prices in Active Markets (Level 1) | Equity mutual funds - international | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		19.7
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. bond funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	48.9
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. bond funds | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	31
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. bond funds | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	11.7
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. government index funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	78.3
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. government index funds | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	59.6
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. government index funds | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	12.1
Pension Plans | Quoted Prices in Active Markets (Level 1) | Global funds (including U.S.)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Quoted Prices in Active Markets (Level 1) | Global funds (including U.S.) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Quoted Prices in Active Markets (Level 1) | Global funds (including U.S.) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Quoted Prices in Active Markets (Level 1) | Derivatives and margin receivable
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0.2
Pension Plans | Quoted Prices in Active Markets (Level 1) | Derivatives and margin receivable | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0.2
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. bond mutual funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		34.8
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. bond mutual funds | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. bond mutual funds | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		22.8
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. government
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		52.9
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. government | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		52.9
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. government | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. corporate
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		143.7
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. corporate | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		143.7
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. municipal
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		4
Pension Plans | Quoted Prices in Active Markets (Level 1) | U.S. municipal | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		4
Pension Plans | Quoted Prices in Active Markets (Level 1) | International
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		44.1
Pension Plans | Quoted Prices in Active Markets (Level 1) | International | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		44.1
Pension Plans | Quoted Prices in Active Markets (Level 1) | International | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Quoted Prices in Active Markets (Level 1) | 103-12 Direct Filing Entities
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Quoted Prices in Active Markets (Level 1) | 103-12 Direct Filing Entities | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Observable Inputs (Level 2)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	270.4	129
Pension Plans | Significant Observable Inputs (Level 2) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	191.2	93.1
Pension Plans | Significant Observable Inputs (Level 2) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	51.4	23.5
Pension Plans | Significant Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Pension Plans | Significant Observable Inputs (Level 2) | Cash and cash equivalents | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Pension Plans | Significant Observable Inputs (Level 2) | Cash and cash equivalents | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Pension Plans | Significant Observable Inputs (Level 2) | Equity funds - global (including U.S.)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	195.6
Pension Plans | Significant Observable Inputs (Level 2) | Equity funds - global (including U.S.) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	137.8
Pension Plans | Significant Observable Inputs (Level 2) | Equity funds - global (including U.S.) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	37.5
Pension Plans | Significant Observable Inputs (Level 2) | Equity index funds - global (including U.S.)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Observable Inputs (Level 2) | Equity index funds - global (including U.S.) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Observable Inputs (Level 2) | Equity index funds - global (including U.S.) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Observable Inputs (Level 2) | Equity mutual funds - U.S.
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		17
Pension Plans | Significant Observable Inputs (Level 2) | Equity mutual funds - U.S. | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		9.1
Pension Plans | Significant Observable Inputs (Level 2) | Equity mutual funds - U.S. | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		5.2
Pension Plans | Significant Observable Inputs (Level 2) | Equity mutual funds - international
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		8.6
Pension Plans | Significant Observable Inputs (Level 2) | Equity mutual funds - international | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		3.3
Pension Plans | Significant Observable Inputs (Level 2) | Equity mutual funds - international | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		3.5
Pension Plans | Significant Observable Inputs (Level 2) | U.S. bond funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Observable Inputs (Level 2) | U.S. bond funds | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Observable Inputs (Level 2) | U.S. bond funds | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Observable Inputs (Level 2) | U.S. government index funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Observable Inputs (Level 2) | U.S. government index funds | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Observable Inputs (Level 2) | U.S. government index funds | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Observable Inputs (Level 2) | Global funds (including U.S.)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	74.8
Pension Plans | Significant Observable Inputs (Level 2) | Global funds (including U.S.) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	53.4
Pension Plans | Significant Observable Inputs (Level 2) | Global funds (including U.S.) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	13.9
Pension Plans | Significant Observable Inputs (Level 2) | Derivatives and margin receivable
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Observable Inputs (Level 2) | Derivatives and margin receivable | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Observable Inputs (Level 2) | U.S. bond mutual funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		73.9
Pension Plans | Significant Observable Inputs (Level 2) | U.S. bond mutual funds | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		73.9
Pension Plans | Significant Observable Inputs (Level 2) | U.S. bond mutual funds | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Observable Inputs (Level 2) | U.S. government
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		9.5
Pension Plans | Significant Observable Inputs (Level 2) | U.S. government | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		6.8
Pension Plans | Significant Observable Inputs (Level 2) | U.S. government | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		1.7
Pension Plans | Significant Observable Inputs (Level 2) | U.S. corporate
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Observable Inputs (Level 2) | U.S. corporate | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Observable Inputs (Level 2) | U.S. municipal
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Observable Inputs (Level 2) | U.S. municipal | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Observable Inputs (Level 2) | International
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		7.5
Pension Plans | Significant Observable Inputs (Level 2) | International | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Observable Inputs (Level 2) | International | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		4.9
Pension Plans | Significant Observable Inputs (Level 2) | 103-12 Direct Filing Entities
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		12.5
Pension Plans | Significant Observable Inputs (Level 2) | 103-12 Direct Filing Entities | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		8.2
Pension Plans | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Equity funds - global (including U.S.)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Equity funds - global (including U.S.) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Equity funds - global (including U.S.) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Equity index funds - global (including U.S.)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Equity index funds - global (including U.S.) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Equity index funds - global (including U.S.) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Equity mutual funds - U.S.
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | Equity mutual funds - U.S. | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | Equity mutual funds - U.S. | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | Equity mutual funds - international
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | Equity mutual funds - international | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | Equity mutual funds - international | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. bond funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. bond funds | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. bond funds | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. government index funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. government index funds | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. government index funds | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Global funds (including U.S.)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Global funds (including U.S.) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Global funds (including U.S.) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Derivatives and margin receivable
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | Derivatives and margin receivable | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. bond mutual funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. bond mutual funds | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. bond mutual funds | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. government
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. government | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. government | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. corporate
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. corporate | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. municipal
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. municipal | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | International
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | International | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | International | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | 103-12 Direct Filing Entities
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Pension Plans | Significant Unobservable Inputs (Level 3) | 103-12 Direct Filing Entities | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets		0
Other Postretirement Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	291	279.8	283.5
Other Postretirement Plans | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	199.2	188.9	189.5
Other Postretirement Plans | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	87	86.4	$ 89.6
Other Postretirement Plans | Cash and cash equivalents
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	3.6	5.3
Other Postretirement Plans | Cash and cash equivalents | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	3	5.2
Other Postretirement Plans | Equity mutual funds - U.S.
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	271.6	258.9
Other Postretirement Plans | Equity mutual funds - U.S. | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	196.2	183.7
Other Postretirement Plans | Equity mutual funds - U.S. | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	72.2	71.8
Other Postretirement Plans | International
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	15.8	15.6
Other Postretirement Plans | International | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	14.8	14.6
Other Postretirement Plans | Quoted Prices in Active Markets (Level 1)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	204	193.4
Other Postretirement Plans | Quoted Prices in Active Markets (Level 1) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	199.2	188.9
Other Postretirement Plans | Quoted Prices in Active Markets (Level 1) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Quoted Prices in Active Markets (Level 1) | Cash and cash equivalents
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	3.6	5.3
Other Postretirement Plans | Quoted Prices in Active Markets (Level 1) | Cash and cash equivalents | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	3	5.2
Other Postretirement Plans | Quoted Prices in Active Markets (Level 1) | Equity mutual funds - U.S.
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	199.4	187.1
Other Postretirement Plans | Quoted Prices in Active Markets (Level 1) | Equity mutual funds - U.S. | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	196.2	183.7
Other Postretirement Plans | Quoted Prices in Active Markets (Level 1) | Equity mutual funds - U.S. | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Quoted Prices in Active Markets (Level 1) | International
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	1	1
Other Postretirement Plans | Quoted Prices in Active Markets (Level 1) | International | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Significant Observable Inputs (Level 2)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	87	86.4
Other Postretirement Plans | Significant Observable Inputs (Level 2) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Significant Observable Inputs (Level 2) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	87	86.4
Other Postretirement Plans | Significant Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Significant Observable Inputs (Level 2) | Cash and cash equivalents | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Significant Observable Inputs (Level 2) | Equity mutual funds - U.S.
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	72.2	71.8
Other Postretirement Plans | Significant Observable Inputs (Level 2) | Equity mutual funds - U.S. | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Significant Observable Inputs (Level 2) | Equity mutual funds - U.S. | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	72.2	71.8
Other Postretirement Plans | Significant Observable Inputs (Level 2) | International
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	14.8	14.6
Other Postretirement Plans | Significant Observable Inputs (Level 2) | International | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	14.8	14.6
Other Postretirement Plans | Significant Unobservable Inputs (Level 3)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Significant Unobservable Inputs (Level 3) | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Significant Unobservable Inputs (Level 3) | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Significant Unobservable Inputs (Level 3) | Equity mutual funds - U.S.
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Significant Unobservable Inputs (Level 3) | Equity mutual funds - U.S. | Spire Missouri
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Significant Unobservable Inputs (Level 3) | Equity mutual funds - U.S. | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Significant Unobservable Inputs (Level 3) | International
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	0	0
Other Postretirement Plans | Significant Unobservable Inputs (Level 3) | International | Spire Alabama
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value measurements of plan assets	$ 0	$ 0

Information by Operating Segm_3

Information by Operating Segment - Additional Information (Details) - 12 months ended Sep. 30, 2020	ReportingUnit	operating-segment
Segment Reporting [Abstract]
Number of reportable segments	2	2

Information by Operating Segm_4

Information by Operating Segment - Schedule of Operating Segment Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Operating Segment Information [Abstract]
Operating Revenues	$ 251.9	$ 321.1	$ 715.5	$ 566.9	$ 225.6	$ 321.3	$ 803.5	$ 602	$ 1,855.4	$ 1,952.4	$ 1,965
Operating Expenses:
Natural gas									696.1	840.3	871.7
Other operation and maintenance									458.6	474.1	477.3
Depreciation and amortization									197.3	181.7	168.4
Taxes, other than income taxes									148.4	154	153.5
Impairments									148.6	0	0
Total Operating Expenses									1,649	1,650.1	1,670.9
Operating Income	0.1	$ (106.5)	$ 210.5	$ 102.3	(25.6)	$ 13.3	$ 209.5	$ 105.1	206.4	302.3	294.1
Net Economic Earnings (Loss)									207.8	195.1	183.7
Capital Expenditures									638.4	823.3	499.4
Total Assets	8,241.2				7,619.2				8,241.2	7,619.2	6,843.6
Eliminations
Operating Segment Information [Abstract]
Operating Revenues									(42.3)	(13.6)	(11.5)
Operating Expenses:
Natural gas									(29.6)	(2.7)	(1.4)
Other operation and maintenance									(12.7)	(10.9)	(10.1)
Total Operating Expenses									(42.3)	(13.6)	(11.5)
Total Assets	(1,101.2)				(1,380.4)				(1,101.2)	(1,380.4)	(1,566.4)
Gas Utility
Operating Segment Information [Abstract]
Operating Revenues									1,751.8	1,859.2	1,888
Gas Utility | Operating Segments
Operating Segment Information [Abstract]
Operating Revenues									1,752	1,860.8	1,888.4
Operating Expenses:
Natural gas									660.2	794.6	842.6
Other operation and maintenance									421.3	441.7	449.7
Depreciation and amortization									189.7	179.4	167
Taxes, other than income taxes									146.5	151.7	152.5
Total Operating Expenses									1,417.7	1,567.4	1,611.8
Operating Income									334.3	293.4	276.6
Net Economic Earnings (Loss)									213.4	199.8	183.1
Capital Expenditures									547.8	565.4	457.7
Total Assets	6,716.2				6,094.6				6,716.2	6,094.6	5,606.7
Gas Utility | Eliminations
Operating Segment Information [Abstract]
Operating Revenues									0.2	1.6	0.4
Gas Marketing
Operating Segment Information [Abstract]
Operating Revenues									87.9	83.7	71.6
Gas Marketing | Operating Segments
Operating Segment Information [Abstract]
Operating Revenues									87.9	83.7	71.6
Operating Expenses:
Natural gas									65.1	47.9	30.2
Other operation and maintenance									11.8	11.7	7.4
Depreciation and amortization									0.6	0.1
Taxes, other than income taxes									1.1	0.8	0.2
Total Operating Expenses									78.6	60.5	37.8
Operating Income									9.3	23.2	33.8
Net Economic Earnings (Loss)									9.1	19.4	22.9
Capital Expenditures									3.6	3.1
Total Assets	182.7				212.3				182.7	212.3	295.3
Corporate, Non-Segment
Operating Segment Information [Abstract]
Operating Revenues									15.7	9.5	5.4
Corporate, Non-Segment | Operating Segments
Operating Segment Information [Abstract]
Operating Revenues									57.8	21.5	16.5
Operating Expenses:
Natural gas									0.4	0.5	0.3
Other operation and maintenance									38.2	31.6	30.3
Depreciation and amortization									7	2.2	1.4
Taxes, other than income taxes									0.8	1.5	0.8
Impairments									148.6
Total Operating Expenses									195	35.8	32.8
Operating Income									(137.2)	(14.3)	(16.3)
Net Economic Earnings (Loss)									(14.7)	(24.1)	(22.3)
Capital Expenditures									87	254.8	41.7
Total Assets	$ 2,443.5				$ 2,692.7				2,443.5	2,692.7	2,508
Corporate, Non-Segment | Eliminations
Operating Segment Information [Abstract]
Operating Revenues									$ 42.1	$ 12	$ 11.1

Information by Operating Segm_5

Information by Operating Segment - Reconciliation of Consolidated Net Economic Earnings to Consolidated Net Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting [Abstract]
Net Income	$ (19.7)	$ (92.3)	$ 133.6	$ 67	$ (34.3)	$ (3)	$ 154.6	$ 67.3	$ 88.6	$ 184.6	$ 214.2
Impairments									148.6	0	0
Provision for ISRS rulings									0	12.2	0
Missouri regulatory adjustments									0	0	30.6
Fair value and timing adjustments									2.5	1.2	(4.3)
Acquisition, divestiture and restructuring activities									0	0.4	13.6
Income tax effect of adjustments									(31.9)	(3.3)	(10.3)
Effect of the Tax Cuts and Jobs Act									0	0	(60.1)
Net Economic Earnings									$ 207.8	$ 195.1	$ 183.7

Regulatory Matters - Schedule o

Regulatory Matters - Schedule of Regulatory Assets and Liabilities, Reflected in Balance Sheets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, current	$ 69.5	$ 78.6
Regulatory assets, non current	1,069.4	767.6
Total Regulatory Assets	1,138.9	846.2
Regulatory liabilities, current	113	60.8
Regulatory liabilities, non current	343.7	399
Total Regulatory Liabilities	456.7	459.8
Pension and Other Postretirement Benefits
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, current	30.6	30.1
Regulatory assets, non current	439.3	416.6
Unamortized Purchased Gas Adjustments
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, current	5.5	18.2
Regulatory assets, non current	12.1	9.1
Other
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, current	33.4	30.3
Regulatory assets, non current	59.3	45
Future Income Taxes Due from Customers
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, non current	123.5	111
Accrued Cost of Removal
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, non current	395.6	150.9
Energy Efficiency
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, non current	39.6	35
Spire Missouri
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, current	32.1	29.4
Regulatory assets, non current	548.7	507.5
Total Regulatory Assets	580.8	536.9
Regulatory liabilities, current	103.2	52.3
Regulatory liabilities, non current	274.8	326.5
Total Regulatory Liabilities	378	378.8
Spire Missouri | Pension and Other Postretirement Benefits
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, current	21.9	21.9
Regulatory assets, non current	332.6	333.3
Spire Missouri | Unamortized Purchased Gas Adjustments
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, current	0	0
Regulatory assets, non current	12.1	9.1
Spire Missouri | Other
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, current	10.2	7.5
Regulatory assets, non current	42.7	27.2
Spire Missouri | Future Income Taxes Due from Customers
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, non current	114.6	102.9
Spire Missouri | Accrued Cost of Removal
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, non current	7.1	0
Spire Missouri | Energy Efficiency
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, non current	39.6	35
Spire Alabama
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, current	20.4	33.9
Regulatory assets, non current	489.9	231.2
Total Regulatory Assets	510.3	265.1
Regulatory liabilities, current	3.9	3.4
Regulatory liabilities, non current	18.5	23
Total Regulatory Liabilities	22.4	26.4
Spire Alabama | Pension and Other Postretirement Benefits
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, current	7.7	7.3
Regulatory assets, non current	98.2	77.2
Spire Alabama | Unamortized Purchased Gas Adjustments
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, current	5.5	17.7
Regulatory assets, non current	0	0
Spire Alabama | Other
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, current	7.2	8.9
Regulatory assets, non current	0.9	0.9
Spire Alabama | Future Income Taxes Due from Customers
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, non current	2.2	2.2
Spire Alabama | Accrued Cost of Removal
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, non current	388.6	150.9
Spire Alabama | Energy Efficiency
Regulatory Asset And Liabilities [Line Items]
Regulatory assets, non current	0	0
Pension and Other Postretirement Benefits
Regulatory Asset And Liabilities [Line Items]
Regulatory liabilities, current	5.8	5.8
Regulatory liabilities, non current	157.6	142.3
Pension and Other Postretirement Benefits | Spire Missouri
Regulatory Asset And Liabilities [Line Items]
Regulatory liabilities, current	3.6	3.6
Regulatory liabilities, non current	140.4	119.1
Pension and Other Postretirement Benefits | Spire Alabama
Regulatory Asset And Liabilities [Line Items]
Regulatory liabilities, current	2.2	2.2
Regulatory liabilities, non current	14.8	19.1
Unamortized Purchased Gas Adjustments
Regulatory Asset And Liabilities [Line Items]
Regulatory liabilities, current	73.1	26.2
Regulatory liabilities, non current	4.4	0
Unamortized Purchased Gas Adjustments | Spire Missouri
Regulatory Asset And Liabilities [Line Items]
Regulatory liabilities, current	72.3	25.4
Regulatory liabilities, non current	4.4	0
Unamortized Purchased Gas Adjustments | Spire Alabama
Regulatory Asset And Liabilities [Line Items]
Regulatory liabilities, current	0	0
Regulatory liabilities, non current	0	0
Other
Regulatory Asset And Liabilities [Line Items]
Regulatory liabilities, current	34.1	28.8
Regulatory liabilities, non current	14.3	35.3
Other | Spire Missouri
Regulatory Asset And Liabilities [Line Items]
Regulatory liabilities, current	27.3	23.3
Regulatory liabilities, non current	8.6	29.2
Other | Spire Alabama
Regulatory Asset And Liabilities [Line Items]
Regulatory liabilities, current	1.7	1.2
Regulatory liabilities, non current	3.7	3.9
Deferred Taxes Due to Customers
Regulatory Asset And Liabilities [Line Items]
Regulatory liabilities, non current	138.8	179.8
Deferred Taxes Due to Customers | Spire Missouri
Regulatory Asset And Liabilities [Line Items]
Regulatory liabilities, non current	121.4	162.5
Deferred Taxes Due to Customers | Spire Alabama
Regulatory Asset And Liabilities [Line Items]
Regulatory liabilities, non current	0	0
Accrued Cost of Removal
Regulatory Asset And Liabilities [Line Items]
Regulatory liabilities, non current	28.6	41.6
Accrued Cost of Removal | Spire Missouri
Regulatory Asset And Liabilities [Line Items]
Regulatory liabilities, non current	0	15.7
Accrued Cost of Removal | Spire Alabama
Regulatory Asset And Liabilities [Line Items]
Regulatory liabilities, non current	$ 0	$ 0

Regulatory Matters - Schedule_2

Regulatory Matters - Schedule of Regulatory Assets Not Earning a Return (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 366.5	$ 334.2
Spire Missouri
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	359.8	328.3
Pension and Other Postretirement Benefits
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	232.3	211.1
Pension and Other Postretirement Benefits | Spire Missouri
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	232.3	211.1
Future Income Taxes Due from Customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	121.3	108.8
Future Income Taxes Due from Customers | Spire Missouri
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	114.6	102.9
Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	12.9	14.3
Other | Spire Missouri
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 12.9	$ 14.3

Regulatory Matters - Additional

Regulatory Matters - Additional Information (Details)	12 Months Ended
	Sep. 30, 2020
Regulated Operations [Abstract]
Remaining recovery period for certain regulatory assets for which no return on investment during recovery period is provided (in years)	20 years
Remaining recovery period for regulatory assets for which no return on investment during recovery period is provided (in years)	15 years

Regulatory Matters - Spire Miss

Regulatory Matters - Spire Missouri - Additional Information (Details) $ / shares in Units, $ in Millions	Nov. 12, 2020USD ($)	Nov. 16, 2019USD ($)	May 25, 2019USD ($)	Apr. 25, 2018USD ($)	Mar. 07, 2018USD ($)$ / shares	Aug. 31, 2020USD ($)	Mar. 31, 2020USD ($)	Sep. 30, 2020USD ($)operating-segment	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Apr. 18, 2018
Public Utilities, General Disclosures [Line Items]
Customer Share								75.00%
Regulatory costs								$ 0	$ 0	$ 30.6
Provision for ISRS rulings								0	12.2	0
Regulatory assets								$ 69.5	78.6
Minimum
Public Utilities, General Disclosures [Line Items]
Customer Share											70.00%
Maximum
Public Utilities, General Disclosures [Line Items]
Customer Share											85.00%
MoPSC | Infrastructure System Replacement Surcharge
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), costs from buildings sold in 2014 excluded from rate base				$ (1.8)
Rate case expenses				(0.9)
Regulatory costs										$ 38.4
After-tax rate reduction to net income					$ 23.6
After-tax rate reduction to earnings per share | $ / shares					$ 0.49
MoPSC | Infrastructure System Replacement Surcharge | Pension Cost
Public Utilities, General Disclosures [Line Items]
Regulatory assets recovery				$ (28.8)
Regulatory costs					$ 30.6
Spire Missouri
Public Utilities, General Disclosures [Line Items]
Number of PGA Discretionary Changes | operating-segment								3
Months between PGA Discretionary Changes								2 months
Customer Share								25.00%
Regulatory assets								$ 32.1	29.4
Spire Missouri | MoPSC
Public Utilities, General Disclosures [Line Items]
Cost savings retention percentage								10.00%
Maximum amount of cost savings allowable								$ 3
Spire Missouri | MoPSC | Infrastructure System Replacement Surcharge
Public Utilities, General Disclosures [Line Items]
Approved rate authorized future annualized revenue								40.3
Payment of customer refund						$ 15
Provision for ISRS rulings									$ 12.2
Additional loss contingency provision of customer refund							$ 4.8
Annual authorized revenue		$ 8.8	$ 12.4
Spire Missouri | MoPSC | Infrastructure System Replacement Surcharge | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Approved rate additional annualized revenue	$ 7
Spire Missouri | MoPSC | Accounting Authority Order
Public Utilities, General Disclosures [Line Items]
Regulatory assets								$ 3.8

Regulatory Matters - Spire Alab

Regulatory Matters - Spire Alabama - Additional Information (Details) - USD ($)	Dec. 01, 2019	Oct. 01, 2018	Jan. 01, 2014	Nov. 30, 2019	Sep. 30, 2020	Sep. 30, 2018	Mar. 24, 2020	Dec. 02, 2019	Sep. 30, 2019	Jan. 15, 2019
Public Utilities, General Disclosures [Line Items]
Amounts returned to customers					$ 113,000,000				$ 60,800,000
Spire Alabama
Public Utilities, General Disclosures [Line Items]
Potential Performance-Based Adjustment, Percent					0.05%
Rate increase (decrease), margin of index range					1.50%
Amounts returned to customers					$ 3,900,000				$ 3,400,000
Regulatory preferred stock and debt securities issuance, amount authorized							$ 150,000,000
APSC | ESR
Public Utilities, General Disclosures [Line Items]
Extraordinary O&M expenses in excess of					1,000,000
Single force majeure					300,000
Multiple force majeures					400,000
Revenue variances					$ 400,000
ESR term					9 years
Underfunded ESR balances amortization term					5 years
ESR annual limitation					$ 700,000
APSC | Spire Alabama
Public Utilities, General Disclosures [Line Items]
Approved return rate on equity		10.40%	10.80%
Maximum return on equity, percentage of prior year revenues					4.00%
Requested rate increase	$ 5,900,000
Return on equity threshold limit exceeded					10.50%
Approved percentage of excess natural gas supply and capacity retain				25.00%
Approved percentage of excess natural gas supply and capacity to customers				75.00%
Gas supply adjustment decrease on annual basis					$ 13,900,000
Rate increase (decrease), margin of index range									1.75%
Approved rate increase (decrease) amount					5,900,000	$ 9,700,000
Line of credit facility borrowing capacity					200,000,000
Principal amount outstanding					25,000,000
Regulatory preferred stock and debt securities issuance, amount authorized					$ 150,000,000			$ 100,000,000		$ 90,000,000
APSC | Spire Alabama | Amount subject to refund
Public Utilities, General Disclosures [Line Items]
Amounts returned to customers						$ 7,200,000			$ 4,200,000
AIM | Spire Alabama
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease) on allowed return on equity, percentage					0.10%
Minimum [Member] | APSC | Spire Alabama
Public Utilities, General Disclosures [Line Items]
Approved return rate on equity		10.15%	10.50%
Equity limitation as percent of capitalization			55.50%
Maximum | APSC | Spire Alabama
Public Utilities, General Disclosures [Line Items]
Approved return rate on equity		10.65%	10.95%
Equity limitation as percent of capitalization			56.50%

Regulatory Matters - Spire - Ad

Regulatory Matters - Spire - Additional Information (Details) - USD ($) $ in Thousands	Oct. 23, 2020	Aug. 28, 2020	Aug. 30, 2019	Sep. 14, 2018	Feb. 01, 2018	Dec. 31, 2015	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Public Utilities, General Disclosures [Line Items]
Regulatory costs							$ 0	$ 0	$ 30,600
Spire Gulf
Public Utilities, General Disclosures [Line Items]
Approved return rate on equity	10.70%						10.70%
Rate increase (decrease), margin of index range							1.50%
Pro-rate rating for equity content							75.00%
Revenue variances							$ 100
Single force majeure							100
Multiple force majeures							$ 150
Recovery percentage of incurred costs							90.00%
Approved point to refund							$ 1,400
Approved rate increase (decrease) amount							1,800
Approved rate increase (decrease), annualized revenue	$ 1,100
Spire
Public Utilities, General Disclosures [Line Items]
Regulatory costs					$ 1,900
Spire Mississippi
Public Utilities, General Disclosures [Line Items]
Approved return rate on equity								9.79%
Excess of allowed return on equity								1.00%
Return on equity shortfall								75.00%
Excess return on equity								50.00%
Recovery period						3 years
APSC | Spire
Public Utilities, General Disclosures [Line Items]
Line of credit facility borrowing capacity							50,000
Principal amount outstanding							$ 25,000
MoPSC
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), annualized revenue		$ 600	$ 300	$ 700
Minimum [Member] | Spire Gulf
Public Utilities, General Disclosures [Line Items]
Approved return rate on equity							10.45%
Maximum | Spire Gulf
Public Utilities, General Disclosures [Line Items]
Approved return rate on equity							10.95%

Commitments and Contingencies -

Commitments and Contingencies - Additional Information - Commitments (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	$ 1,745.4
Outstanding mortgage loans incurred in connection with various real estate ventures with general partners		$ 1.2
Spire Missouri
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	1,410.3
Spire Missouri | Purchase Commitment | Subsidiary of Common Parent
Long-term Purchase Commitment [Line Items]
Annual purchase commitment	$ 1
Commitment termination date	Mar. 31, 2021
Spire Alabama
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	$ 229.7

Commitments and Contingencies_2

Commitments and Contingencies - Additional Information - Contingencies (Details) - site	Sep. 30, 2019	Sep. 30, 2013
Spire Missouri East
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP) sites in Missouri	3
Number of sites enrolled in Brownfields/Voluntary clean up program	2
Spire Missouri East | Previous Ownership
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP)		19
Spire Missouri West | Previous Ownership
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP)	7
Spire Alabama
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP)	9
Number of former manufactured gas distribution	5
Spire Alabama | Current Ownership
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP)	4
Number of former manufactured gas distribution	1

Leases - Additional Information

Leases - Additional Information (Details)	12 Months Ended
	Sep. 30, 2020
Lessee Lease Description [Line Items]
Operating lease, existence of option to extend	true
Operating lease, option to extend	The lease agreement covering the Company’s primary office space in St. Louis extends through February 2035, with an option to renew for an additional five years
Operating lease extend period	2028-12
Operating lease, renewal term	5 years
Operating lease, existence of option to terminate	true
Operating lease, existence of option to terminate period	with options to terminate three years
Spire Missouri
Lessee Lease Description [Line Items]
Operating lease, existence of option to extend	true
Operating lease, option to extend	The lease agreement covering Spire Marketing and Spire Storage office space in Houston extends through December 2028, with options to terminate three years earlier or to renew for an additional five years
Operating lease extend period	2035-02
Operating lease, renewal term	5 years
Spire Alabama
Lessee Lease Description [Line Items]
Operating lease, existence of option to extend	true
Operating lease, option to extend	Spire Alabama’s lease agreement for office space in Birmingham extends through January 2024.
Operating lease extend period	2024-01

Leases - Operating Lease Cost C

Leases - Operating Lease Cost Cash Flow and Noncash Information (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)
Lessee Lease Description [Line Items]
Operating lease cost, including amounts capitalized	$ 8.7
Cash flow and noncash information about operating leases:
Operating cash flows representing cash paid for amounts included in the measurement of lease liabilities	8.5
Right-of-use assets obtained in exchange for lease liabilities	71.1
Spire Missouri Inc
Lessee Lease Description [Line Items]
Operating lease cost, including amounts capitalized	0.5
Cash flow and noncash information about operating leases:
Operating cash flows representing cash paid for amounts included in the measurement of lease liabilities	0.5
Right-of-use assets obtained in exchange for lease liabilities	2.1
Spire Alabama
Lessee Lease Description [Line Items]
Operating lease cost, including amounts capitalized	3.5
Cash flow and noncash information about operating leases:
Operating cash flows representing cash paid for amounts included in the measurement of lease liabilities	3.3
Right-of-use assets obtained in exchange for lease liabilities	$ 10

Leases - Summary of Balance She

Leases - Summary of Balance Sheet and Weighted-Average Information about Operating Leases (Details) $ in Millions	Sep. 30, 2020USD ($)
Lessee Lease Description [Line Items]
Right-of-use assets	$ 65.1
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent
Lease liabilities, current	$ 6.5
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent
Lease liabilities, noncurrent	$ 58.4
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent
Weighted-average remaining lease term	15 years 10 months 24 days
Weighted-average discount rate	4.20%
Spire Missouri Inc
Lessee Lease Description [Line Items]
Right-of-use assets	$ 1.7
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent
Lease liabilities, current	$ 0.3
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent
Lease liabilities, noncurrent	$ 1.4
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent
Weighted-average remaining lease term	5 years 3 months 18 days
Weighted-average discount rate	2.50%
Spire Alabama
Lessee Lease Description [Line Items]
Right-of-use assets	$ 6.7
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent
Lease liabilities, current	$ 1.9
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent
Lease liabilities, noncurrent	$ 4.7
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent
Weighted-average remaining lease term	3 years 3 months 18 days
Weighted-average discount rate	2.20%

Leases - Schedule of Maturity A

Leases - Schedule of Maturity Analysis for Operating Lease Liabilities (Details) $ in Millions	Sep. 30, 2020USD ($)
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2021	$ 6.6
2022	7.2
2023	7.2
2024	5.8
2025	5.1
Thereafter	58.4
Total undiscounted lease payments	90.3
Less present value discount	(25.4)
Total current and noncurrent lease liabilities	64.9
Spire Missouri Inc
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2021	0.3
2022	0.4
2023	0.3
2024	0.3
2025	0.3
Thereafter	0.2
Total undiscounted lease payments	1.8
Less present value discount	(0.1)
Total current and noncurrent lease liabilities	1.7
Spire Alabama
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2021	1.9
2022	2.1
2023	2.1
2024	0.7
Total undiscounted lease payments	6.8
Less present value discount	(0.2)
Total current and noncurrent lease liabilities	$ 6.6

Leases - Schedule of Annual Min

Leases - Schedule of Annual Minimum Rental Commitments for Operating Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Aggregate Rental Expense	$ 10.9	$ 10
2020	8.2
2021	7
2022	6.8
2023	6.1
2024	4.8
Later	36.5
Total	69.4
Spire Missouri Inc
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Aggregate Rental Expense	3.7	3.6
2020	0.5
2021	0.2
Total	0.7
Spire Alabama
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Aggregate Rental Expense	5.2	$ 4.7
2020	2.9
2021	2.1
2022	2.1
2023	2.1
2024	0.7
Total	$ 9.9

Interim Financial Information_3

Interim Financial Information (Unaudited) - Schedule of Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Quarterly Financial Information [Line Items]
Total operating revenues	$ 251.9	$ 321.1	$ 715.5	$ 566.9	$ 225.6	$ 321.3	$ 803.5	$ 602	$ 1,855.4	$ 1,952.4	$ 1,965
Operating Income (Loss)	0.1	(106.5)	210.5	102.3	(25.6)	13.3	209.5	105.1	206.4	302.3	294.1
Net Income (Loss)	$ (19.7)	$ (92.3)	$ 133.6	$ 67	$ (34.3)	$ (3)	$ 154.6	$ 67.3	$ 88.6	$ 184.6	$ 214.2
Basic Earnings (Loss) Per Share of Common Stock	$ (0.45)	$ (1.87)	$ 2.55	$ 1.24	$ (0.75)	$ (0.09)	$ 3.05	$ 1.33	$ 1.44	$ 3.53	$ 4.35
Diluted Earnings (Loss) Per Share of Common Stock	$ (0.45)	$ (1.87)	$ 2.54	$ 1.24	$ (0.74)	$ (0.09)	$ 3.04	$ 1.32	$ 1.44	$ 3.52	$ 4.33
Spire Missouri
Quarterly Financial Information [Line Items]
Total operating revenues	$ 158.2	$ 203.9	$ 457.5	$ 374	$ 130.6	$ 191.4	$ 556.6	$ 413.2	$ 1,193.6	$ 1,291.8	$ 1,285.6
Operating Income (Loss)	13.9	7	117.7	67	(11.2)	12.2	102.4	71.4	205.6	174.8	158.5
Net Income (Loss)	1.2	6.5	74.5	48	(17.3)	1.1	80	51.2	130.2	115	129.3
Spire Alabama
Quarterly Financial Information [Line Items]
Total operating revenues	62.1	81.2	185.5	126.2	60.8	90.8	180.4	133.5	455	465.5	500.7
Operating Income (Loss)	(8.5)	9.3	81.2	20.9	(12.3)	11.1	79.6	17.1	102.9	95.5	96.6
Net Income (Loss)	$ (8.9)	$ 3.6	$ 57.8	$ 13.2	$ (12.3)	$ 5.6	$ 56.7	$ 10.3	$ 65.7	$ 60.3	$ 1.3