Capitalization and Short-Term Borrowings - Narrative (Details)			3 Months Ended	12 Months Ended
	May 18, 2023 USD ($)	Feb. 24, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2022 USD ($) $ / shares shares	Sep. 30, 2021 USD ($) $ / shares shares	Mar. 31, 2023 USD ($)	Nov. 25, 2022 USD ($)	Oct. 27, 2022 USD ($)	Jun. 30, 2022 USD ($) bank	May 03, 2022 bank	Feb. 28, 2022 USD ($) bank	Mar. 11, 2021 USD ($)
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
Common stock issued as a result of SARs exercises (in shares) | shares				12,055
Shares tendered (in shares) | shares				103,059
Stock-based compensation expense				$ 18,600,000	$ 17,600,000	$ 15,200,000
Tax benefit related to stock-based compensation expense				2,400,000	2,500,000	2,400,000
Capitalized stock-based compensation costs				100,000	100,000	100,000
Tax benefit related to stock-based compensation exercises and vestings				$ 1,200,000
Number of shares available for future grant (in shares) | shares				1,510,900
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				$ 297,306,000	0	495,267,000
Repayments of short-term borrowings				250,000,000	0	0
Early redemption premium paid				0	0	$ 15,715,000
Principal amounts of long-term debt maturing in 2024				0
Principal amounts of long-term debt maturing in 2025				500,000,000
Principal amounts of long-term debt maturing in 2026				500,000,000
Principal amounts of long-term debt maturing in 2027				600,000,000
Principal amounts of long-term debt maturing in 2028				300,000,000
Principal amounts of long-term debt maturing after 2028				500,000,000
Commercial paper, outstanding				287,500,000	0
Short-term notes payable outstanding to banks				$ 0	$ 60,000,000
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				381,400,000
Committed credit facility debt to capitalization ratio ceiling test impairment adjustment				190,700,000
Debt to capitalization ratio maximum excluded unrealized gains or losses on other derivative financial instruments in AOCI				$ 10,000,000
Debt to capitalization ratio				0.46
Permitted additional short-term and/or long-term debt to be outstanding under the Credit Agreement				$ 3,170,000,000
Aggregated indebtedness				$ 40,000,000
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%
Maximum debt increase under existing indenture covenants				$ 3,430,000,000
Long-Term debt issued under 1974 Indenture as a percent of total long-term debt				2.10%
Commercial Paper
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Weighted average interest rate				6.13%
364-Day Credit Agreement
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Repayments of short-term borrowings				$ 250,000,000
Number of banks in syndicate | bank										5
Maximum borrowing capacity										$ 250,000,000
Committed credit facility amount drawn									$ 250,000,000
Credit Agreement
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Number of banks in syndicate | bank											12	12
Maximum borrowing capacity												$ 1,000,000,000
5.50% Notes Due October 1, 2026
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Long-term debt, face value	$ 300,000,000			$ 300,000,000
Long-term debt, interest rate	5.50%			5.50%
Net proceeds from issuance of long-term debt	$ 297,300,000
2.95% Notes Due March 1, 2031
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Long-term debt, face value		$ 500,000,000		$ 500,000,000
Long-term debt, interest rate		2.95%		2.95%
Net proceeds from issuance of long-term debt		$ 495,300,000
4.90% Notes Due December 1, 2021
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Long-term debt, face value													$ 500,000,000
Long-term debt, interest rate													4.90%
Debt instrument redeemed													$ 515,700,000
Early redemption premium paid			$ 15,700,000
3.75% Notes Due March 2023
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Long-term debt, interest rate					3.75%		3.75%	3.75%
Debt instrument redeemed							$ 350,000,000	$ 150,000,000
Commercial Paper
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Amount available to be issued under commercial paper program				$ 500,000,000
Notes Payable to Banks
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Weighted average interest rate					4.02%
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
Board Of Directors
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Common stock issued (in shares) | shares				31,715
Officers
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Common stock issued (in shares) | shares				2,796
Restricted Stock Units (RSUs)
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Common stock issued (in shares) | shares				119,147
Performance Shares
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Common stock issued (in shares) | shares				278,687
SARs vested in period (in shares) | shares				278,687
Number of shares granted (in shares) | shares				202,259	195,397	309,470
Weighted average fair value of award (in dollars per share) | $ / shares				$ 64.28	$ 65.39	$ 39.19
Unrecognized compensation expense				$ 12,800,000
Unrecognized compensation expense recognized weighted average period				1 year 8 months 12 days
Performance Shares | 2024
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares				214,158
Performance Shares | 2025
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares				179,320
Performance Shares | 2026
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares				193,313
Stock Appreciation Rights (SARs)
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Number of shares granted (in shares) | shares				0	0	0
Intrinsic value of SARs exercised				$ 800,000	$ 2,000,000
Number of SARs exercised (in shares) | shares				72,008		0
SARs vested in period (in shares) | shares				0	0	0
Non-Performance Based Restricted Stock Units (RSUs)
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
SARs vested in period (in shares) | shares				119,147
Number of shares granted (in shares) | shares				133,173	128,950	172,513
Weighted average fair value of award (in dollars per share) | $ / shares				$ 58.10	$ 54.10	$ 37.98
Unrecognized compensation expense				$ 7,500,000
Unrecognized compensation expense recognized weighted average period				2 years 2 months 12 days
Non-Performance Based Restricted Stock Units (RSUs) | 2024
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Non-vested stock-based compensation lapse (in shares) | shares				115,652
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				98,343
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				79,021
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				33,527
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				15,643
ROC Performance Shares
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Performance shares calculation period				3 years	3 years	3 years
ESG Performance Shares
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Number of shares granted (in shares) | shares						0
Performance shares calculation period				3 years	3 years	3 years
TSR Performance Shares
Schedule of Capitalization, Long-Term Debt and Equity [Line Items]
Performance shares calculation period				3 years	3 years	3 years