Debt - Narrative (Details)									1 Months Ended			12 Months Ended
	Jun. 26, 2025 USD ($)	Apr. 01, 2025 USD ($)	Mar. 31, 2025 USD ($)	Oct. 01, 2024 USD ($)	Jun. 21, 2024 USD ($)	Mar. 28, 2024 USD ($)	Mar. 27, 2024 USD ($)	Oct. 10, 2023 USD ($)	Sep. 30, 2025 USD ($) credit_facility	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2025 USD ($) credit_facility	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Oct. 01, 2025 USD ($)
Debt Instrument [Line Items]
Proceeds from issuance long term debt												$ 1,143,447,000	$ 1,240,204,000	$ 797,258,000
Offering received												$ 122,874,000	231,138,000	$ 171,145,000
Ratio of total debt to total capitalization maximum												70.00%
Ratio of indebtedness to net capital									0.41			0.41
Minimum
Debt Instrument [Line Items]
Outstanding indebtedness									$ 15,000,000			$ 15,000,000
Maximum
Debt Instrument [Line Items]
Outstanding indebtedness									100,000,000			$ 100,000,000
Senior Notes
Debt Instrument [Line Items]
Offering received									122,900,000	$ 231,100,000	$ 171,100,000
Unsecured 5.45% Senior Notes, Due January 2056 | Senior Notes
Debt Instrument [Line Items]
Proceeds from issuance long term debt									$ 589,800,000
Unsecured 5.45% Senior Notes, Due January 2056 | Senior Notes | Subsequent Event
Debt Instrument [Line Items]
Debt face amount															$ 600,000,000
Interest rate															5.45%
Effective rate															4.85%
Unsecured 5.20% Senior Notes, due August 2035
Debt Instrument [Line Items]
Interest rate									5.20%			5.20%
Unsecured 5.20% Senior Notes, due August 2035 | Senior Notes
Debt Instrument [Line Items]
Debt face amount	$ 500,000,000
Interest rate	5.20%
Effective rate	5.35%
Proceeds from issuance long term debt	$ 493,700,000
Unsecured 5.00% Senior Notes, due December 2054
Debt Instrument [Line Items]
Interest rate									5.00%			5.00%
Unsecured 5.00% Senior Notes, due December 2054 | Senior Notes
Debt Instrument [Line Items]
Debt face amount				$ 650,000,000
Interest rate				5.00%
Effective rate				3.90%
Proceeds from issuance long term debt				$ 639,400,000
Unsecured 5.90% Senior Notes, due November 2033
Debt Instrument [Line Items]
Interest rate									5.90%			5.90%
Unsecured 5.90% Senior Notes, due November 2033 | Senior Notes
Debt Instrument [Line Items]
Debt face amount					$ 325,000,000			$ 400,000,000
Interest rate					5.90%			5.90%
Effective rate					5.17%			4.35%
Proceeds from issuance long term debt					$ 339,000,000
Unsecured 6.20% Senior Notes, due November 2053
Debt Instrument [Line Items]
Interest rate									6.20%			6.20%
Unsecured 6.20% Senior Notes, due November 2053 | Senior Notes
Debt Instrument [Line Items]
Debt face amount								$ 500,000,000
Interest rate								6.20%
Effective rate								5.56%
Unsecured Senior Notes Due 2033 and Unsecured Senior Notes Due 2053 | Senior Notes
Debt Instrument [Line Items]
Proceeds from issuance of debt								$ 889,400,000
Five Year Unsecured Revolving Credit Agreement, Maturing On March 28, 2029 | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread percent												0.00%
Five Year Unsecured Revolving Credit Agreement, Maturing On March 28, 2029 | Minimum | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread percent												0.75%
Five Year Unsecured Revolving Credit Agreement, Maturing On March 28, 2029 | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread percent												0.25%
Five Year Unsecured Revolving Credit Agreement, Maturing On March 28, 2029 | Maximum | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread percent												1.25%
Five Year Unsecured Revolving Credit Agreement, Maturing On March 28, 2029 | Commercial Paper
Debt Instrument [Line Items]
Maximum borrowing capacity									$ 1,500,000,000			$ 1,500,000,000
Credit facility, accordion feature									250,000,000			250,000,000
Loan increase potential									1,750,000,000			1,750,000,000
Five Year Unsecured Revolving Credit Agreement, Maturing On March 28, 2029 | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity									$ 3,100,000,000			$ 3,100,000,000
Number of credit facilities | credit_facility									4			4
Five Year Unsecured Revolving Credit Agreement
Debt Instrument [Line Items]
Commercial paper									$ 0			$ 0
Five Year Unsecured Revolving Credit Agreement | Commercial Paper
Debt Instrument [Line Items]
Maximum borrowing capacity							$ 1,500,000,000
Debt term							5 years
$1.5 Billion Revolving Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity						$ 1,500,000,000
Debt term						3 years
Credit facility, accordion feature						$ 250,000,000
Loan increase potential						$ 1,750,000,000
Line of credit borrowings outstanding									0	0		$ 0	0
$1.5 Billion Revolving Credit Facility | Revolving Credit Facility | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread percent												0.00%
$1.5 Billion Revolving Credit Facility | Revolving Credit Facility | Minimum | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread percent												0.75%
$1.5 Billion Revolving Credit Facility | Revolving Credit Facility | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread percent												0.25%
$1.5 Billion Revolving Credit Facility | Revolving Credit Facility | Maximum | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread percent												1.25%
$900 Million Revolving Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit borrowings outstanding									0	0		$ 0	0
$50 Million Bank Loan Agreement | Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 50,000,000
Debt term		364 days
Line of credit borrowings outstanding									0	$ 0		0	$ 0
$50 Million Revolving Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 50,000,000
Debt term			364 days
Line of credit borrowings outstanding									0			0
Remaining borrowing capacity									$ 44,400,000			$ 44,400,000