Capitalization and Short-Term Borrowings - Narrative (Details)		12 Months Ended
	May 18, 2023 USD ($)	Sep. 30, 2024 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2022 USD ($) $ / shares shares	May 31, 2024 USD ($) bank	Apr. 01, 2024 USD ($)	Mar. 08, 2024 USD ($)	Feb. 29, 2024 bank	Feb. 14, 2024 USD ($) lender	Feb. 28, 2022 USD ($) bank
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Common stock issued for 401(k) plans (in shares) | shares		0
Common stock issued for the Direct Stock Purchase and Dividend Reinvestment Plan (in shares) | shares		0
Stock repurchase program, authorized amount							$ 200,000,000
Stock-based compensation expense		$ 19,800,000	$ 18,600,000	$ 17,600,000
Tax benefit related to stock-based compensation expense		2,500,000	2,400,000	2,500,000
Capitalized stock-based compensation costs		100,000	100,000	100,000
Tax benefit related to stock-based compensation exercises and vestings		$ 300,000
Number of shares available for future grant (in shares) | shares		3,889,027
Preferred stock shares authorized (in shares) | shares		10,000,000
Preferred stock par value (in dollars per share) | $ / shares		$ 1
Net proceeds from issuance of long-term debt		$ 299,359,000	297,306,000	0
Repayments of short-term borrowings		0	250,000,000	$ 0
Principal amounts of long-term debt maturing in 2025		500,000,000
Principal amounts of long-term debt maturing in 2026		800,000,000.0
Principal amounts of long-term debt maturing in 2027		600,000,000.0
Principal amounts of long-term debt maturing in 2028		300,000,000.0
Principal amounts of long-term debt maturing in 2029		0
Principal amounts of long-term debt maturing after 2029		500,000,000.0
Commercial paper, outstanding		90,700,000	287,500,000
Short-term notes payable outstanding to banks		$ 0	0
Committed debt to capitalization ratio		0.65
Ceiling test impairment adjustment (as a percent)		50.00%
Ceiling test impairment maximum adjustment		$ 400,000,000
Cumulative after-tax ceiling test impairments since July 1, 2018		717,900,000
Committed credit facility debt to capitalization ratio ceiling test impairment adjustment		358,900,000
Debt to capitalization ratio maximum excluded unrealized gains or losses on other derivative financial instruments in AOCI		$ 10,000,000
Debt to capitalization ratio		0.47
Permitted additional short-term and/or long-term debt to be outstanding under the Credit Agreement		$ 3,070,000,000.00
Aggregated indebtedness		$ 40,000,000.0
Indenture Test Period		12 months
Indenture period before debt issuance		15 months
Maximum long-term debt to consolidated asset ratio under indenture (as a percent)		60.00%
Stock And Benefit Plans
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Shares repurchased (in shares) | shares		78,141
Share Repurchase Plan
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Shares repurchased (in shares) | shares		1,146,259
Share repurchase program, average price per share (in USD per share) | $ / shares		$ 56.32
Share Repurchases		$ 65,200,000
364-Day Credit Agreement
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Repayments of short-term borrowings			$ 250,000,000
Credit Agreement
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Maximum borrowing capacity					$ 1,000,000,000					$ 1,000,000,000
Number of banks in syndicate | bank					3			11		12
Term Loan Agreement
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Long-term debt, face amount						$ 300,000,000
Net proceeds from issuance of long-term debt		$ 299,400,000
Rate adjustment to SOFR		0.0010
Spread on variable rate		1.375%
Debt instruments, number of lenders | lender									6
Maximum borrowing capacity									$ 300,000,000
Commercial Paper
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Amount available to be issued under commercial paper program		$ 500,000,000.0
Weighted average interest rate		5.30%	6.13%
5.50% Notes Due October 1, 2026
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Long-term debt, face amount	$ 300,000,000	$ 300,000,000
Net proceeds from issuance of long-term debt	$ 297,300,000
Long-term debt, interest rate	5.50%	5.50%
Indenture From 1974
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Carrying amount of long-term debt under 1974 indenture		$ 50,000,000
Interest payments Remaining		$ 3,200,000
Board Of Directors
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Common stock issued (in shares) | shares		36,078
Officer DCP Plan
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Common stock issued (in shares) | shares		8,318
Restricted Stock Units (RSUs)
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Common stock issued (in shares) | shares		115,337
Performance Shares
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Common stock issued (in shares) | shares		251,255
Number of shares granted (in shares) | shares		361,729	202,259	195,397
Weighted average fair value of award (in dollars per share) | $ / shares		$ 44.23	$ 64.28	$ 65.39
Unrecognized compensation expense		$ 15,700,000
Unrecognized compensation expense recognized weighted average period		2 years 4 months 24 days
Performance Shares | 2025
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares		177,118
Performance Shares | 2026
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares		188,767
Performance Shares | 2027
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares		297,392
Performance Shares | 2028
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares		0
Performance Shares | 2029
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares		0
Performance Shares | Thereafter
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares		56,300
Non-Performance Based Restricted Stock Units (RSUs)
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Number of shares granted (in shares) | shares		220,778	133,173	128,950
Weighted average fair value of award (in dollars per share) | $ / shares		$ 42.44	$ 58.10	$ 54.10
Unrecognized compensation expense		$ 9,200,000
Unrecognized compensation expense recognized weighted average period		3 years
Non-Performance Based Restricted Stock Units (RSUs) | 2025
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares		129,688
Non-Performance Based Restricted Stock Units (RSUs) | 2026
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares		111,557
Non-Performance Based Restricted Stock Units (RSUs) | 2027
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares		86,667
Non-Performance Based Restricted Stock Units (RSUs) | 2028
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares		34,757
Non-Performance Based Restricted Stock Units (RSUs) | 2029
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares		19,228
Non-Performance Based Restricted Stock Units (RSUs) | Thereafter
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares		56,296
ROC Performance Shares | Three Year Performance Cycle
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Performance shares calculation period		3 years	3 years	3 years
ROC Performance Shares | Five Year Performance Cycle
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Performance shares calculation period		5 years	5 years	5 years
ESG Performance Shares | Three Year Performance Cycle
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Performance shares calculation period		3 years	3 years	3 years
TSR Performance Shares | Three Year Performance Cycle
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Performance shares calculation period		3 years	3 years	3 years
TSR Performance Shares | Five Year Performance Cycle
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Performance shares calculation period		5 years	5 years	5 years