Debt - Narrative (Details)						9 Months Ended
	Jun. 30, 2024 USD ($) creditFacility	Apr. 01, 2024 USD ($)	Mar. 28, 2024 USD ($)	Mar. 27, 2024 USD ($)	Oct. 10, 2023 USD ($)	Jun. 30, 2024 USD ($) creditFacility	Jun. 30, 2023 USD ($)	Jun. 21, 2024 USD ($)	Sep. 30, 2023 USD ($)
Line Of Credit Facility [Line Items]
Proceeds from issuance of long-term debt						$ 1,240,204,000	$ 797,258,000
Maximum debt-to-total-capitalization ratio						70.00%
Debt-to-total-capitalization ratio	0.40					0.40
Minimum
Line Of Credit Facility [Line Items]
Outstanding indebtedness	$ 15,000,000					$ 15,000,000
Maximum
Line Of Credit Facility [Line Items]
Outstanding indebtedness	$ 100,000,000					$ 100,000,000
Unsecured Senior Notes Due 2053 and Unsecured Senior Notes Due 2033 | Senior Notes
Line Of Credit Facility [Line Items]
Proceeds from issuance of long-term debt					$ 889,400,000
Unsecured 6.20% Senior Notes, due October 2053
Line Of Credit Facility [Line Items]
Interest rate	6.20%					6.20%
Unsecured 6.20% Senior Notes, due October 2053 | Senior Notes
Line Of Credit Facility [Line Items]
Debt face amount					$ 500,000,000
Interest rate					6.20%
Effective rate					5.56%
Unsecured 5.90% Senior Notes, due October 2033
Line Of Credit Facility [Line Items]
Interest rate	5.90%					5.90%
Unsecured 5.90% Senior Notes, due October 2033 | Senior Notes
Line Of Credit Facility [Line Items]
Debt face amount					$ 400,000,000			$ 325,000,000
Interest rate					5.90%			5.90%
Effective rate					4.35%			5.17%
Proceeds from issuance of long-term debt	$ 339,700,000
Five Year Unsecured Revolving Credit Agreement
Line Of Credit Facility [Line Items]
Outstanding commercial paper									$ 241,900,000
Five Year Unsecured Revolving Credit Agreement | Commercial Paper
Line Of Credit Facility [Line Items]
Maximum borrowing capacity				$ 1,500,000,000
Debt agreement term				5 years
Five Year Unsecured Revolving Credit Agreement, March 28, 2029
Line Of Credit Facility [Line Items]
Outstanding commercial paper	0					$ 0
Five Year Unsecured Revolving Credit Agreement, March 28, 2029 | Minimum | Base Rate
Line Of Credit Facility [Line Items]
Interest rate spread						0.00%
Five Year Unsecured Revolving Credit Agreement, March 28, 2029 | Minimum | Term SOFR
Line Of Credit Facility [Line Items]
Interest rate spread						0.75%
Five Year Unsecured Revolving Credit Agreement, March 28, 2029 | Maximum | Base Rate
Line Of Credit Facility [Line Items]
Interest rate spread						0.25%
Five Year Unsecured Revolving Credit Agreement, March 28, 2029 | Maximum | Term SOFR
Line Of Credit Facility [Line Items]
Interest rate spread						1.25%
Five Year Unsecured Revolving Credit Agreement, March 28, 2029 | Commercial Paper
Line Of Credit Facility [Line Items]
Maximum borrowing capacity	1,500,000,000		$ 1,500,000,000			$ 1,500,000,000
Debt agreement term			5 years
Accordion feature			$ 250,000,000
Maximum borrowing capacity post accordion feature			1,750,000,000
Five Year Unsecured Revolving Credit Agreement, March 28, 2029 | Revolving Credit Facility
Line Of Credit Facility [Line Items]
Maximum borrowing capacity	$ 3,100,000,000					$ 3,100,000,000
Number of credit facilities | creditFacility	4					4
$900 Million Revolving Credit Facility | Revolving Credit Facility
Line Of Credit Facility [Line Items]
Maximum borrowing capacity				$ 900,000,000
Debt agreement term				3 years
Outstanding borrowings									0
$1.5 Billion Revolving Credit Facility | Revolving Credit Facility
Line Of Credit Facility [Line Items]
Maximum borrowing capacity			$ 1,500,000,000
Debt agreement term			3 years
Accordion feature			$ 250,000,000
Maximum borrowing capacity post accordion feature			$ 1,750,000,000
Outstanding borrowings	$ 0					$ 0
$1.5 Billion Revolving Credit Facility | Revolving Credit Facility | Minimum | Base Rate
Line Of Credit Facility [Line Items]
Interest rate spread						0.00%
$1.5 Billion Revolving Credit Facility | Revolving Credit Facility | Minimum | Term SOFR
Line Of Credit Facility [Line Items]
Interest rate spread						0.75%
$1.5 Billion Revolving Credit Facility | Revolving Credit Facility | Maximum | Base Rate
Line Of Credit Facility [Line Items]
Interest rate spread						0.25%
$1.5 Billion Revolving Credit Facility | Revolving Credit Facility | Maximum | Term SOFR
Line Of Credit Facility [Line Items]
Interest rate spread						1.25%
$50 Million Bank Loan Agreement | Line of Credit
Line Of Credit Facility [Line Items]
Maximum borrowing capacity		$ 50,000,000
Debt agreement term		364 days
Outstanding borrowings	0					$ 0			$ 0
$50 Million Revolving Credit Facility
Line Of Credit Facility [Line Items]
Outstanding borrowings	0					0
$50 Million Revolving Credit Facility | Revolving Credit Facility
Line Of Credit Facility [Line Items]
Maximum borrowing capacity	50,000,000					$ 50,000,000
Debt agreement term						364 days
Remaining borrowing capacity	$ 44,400,000					$ 44,400,000