Debt - Narrative (Details)		6 Months Ended
	Oct. 01, 2024 USD ($)	Mar. 31, 2025 USD ($) credit_facility	Mar. 31, 2024 USD ($)	Sep. 30, 2024 USD ($)
Line Of Credit Facility [Line Items]
Proceeds from issuance of long-term debt		$ 645,372,000	$ 898,275,000
Maximum debt-to-total-capitalization ratio		70.00%
Debt-to-total-capitalization ratio		0.40
Minimum
Line Of Credit Facility [Line Items]
Outstanding indebtedness		$ 15,000,000
Maximum
Line Of Credit Facility [Line Items]
Outstanding indebtedness		$ 100,000,000
Unsecured 5.00% Senior Notes, due December 2054
Line Of Credit Facility [Line Items]
Interest rate		5.00%
Unsecured 5.00% Senior Notes, due December 2054 | Senior Notes
Line Of Credit Facility [Line Items]
Debt face amount	$ 650,000,000
Interest rate	5.00%
Effective rate	3.90%
Proceeds from issuance of long-term debt	$ 639,400,000
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
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
Number of credit facilities | credit_facility		4
$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
$50 Million Revolving Credit Facility
Line Of Credit Facility [Line Items]
Outstanding borrowings		0
$50 Million Revolving Credit Facility | Revolving Credit Facility
Line Of Credit Facility [Line Items]
Maximum borrowing capacity		$ 50,000,000
Debt agreement term		364 days
Remaining borrowing capacity		$ 44,400,000