Debt - Narrative (Details)				6 Months Ended
	Mar. 09, 2023 USD ($)	Mar. 03, 2023 USD ($)	Oct. 03, 2022 USD ($)	Mar. 31, 2023 USD ($) creditFacility	Mar. 31, 2022 USD ($)	Sep. 30, 2022 USD ($)	Mar. 31, 2021 USD ($)
Line Of Credit Facility [Line Items]
Proceeds from issuance of long-term debt				$ 797,258,000	$ 798,802,000
Repayment of long-term debt				$ 2,200,000,000	$ 200,000,000
Maximum debt-to-total-capitalization ratio				70.00%
Debt-to-total-capitalization ratio				0.40
Revolving Credit Facility
Line Of Credit Facility [Line Items]
Maximum borrowing capacity				$ 2,500,000,000
Number of credit facilities | creditFacility				4
Minimum
Line Of Credit Facility [Line Items]
Outstanding indebtedness				$ 15,000,000
Maximum
Line Of Credit Facility [Line Items]
Outstanding indebtedness				100,000,000
Senior Notes
Line Of Credit Facility [Line Items]
Debt instrument, face amount							$ 2,200,000,000
Repayment of long-term debt		$ 2,200,000,000
Unsecured Debt | Line of Credit
Line Of Credit Facility [Line Items]
Repayment of long-term debt	$ 1,100,000,000
Unsecured Senior Notes Due October 2052 | Senior Notes
Line Of Credit Facility [Line Items]
Debt instrument, face amount			$ 500,000,000
Interest rate			5.75%
Effective interest rate			4.50%
Unsecured Senior Notes Due October 2032 | Senior Notes
Line Of Credit Facility [Line Items]
Debt instrument, face amount			$ 300,000,000
Interest rate			5.45%
Effective interest rate			5.57%
Unsecured Senior Notes Due Octpber 2032 and Unsecured Senior Notes Due October 2052 | Senior Notes
Line Of Credit Facility [Line Items]
Proceeds from issuance of long-term debt			$ 789,400,000
Five Year Unsecured Revolving Credit Agreement
Line Of Credit Facility [Line Items]
Outstanding commercial paper				0		$ 185,000,000
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
Accordion feature				$ 250,000,000
Maximum borrowing capacity post accordion feature				$ 1,750,000,000
Five Year Unsecured Revolving Credit Agreement | Minimum | Base Rate
Line Of Credit Facility [Line Items]
Interest rate spread				0.00%
Five Year Unsecured Revolving Credit Agreement | Minimum | SOFR
Line Of Credit Facility [Line Items]
Interest rate spread				0.75%
Five Year Unsecured Revolving Credit Agreement | Maximum | Base Rate
Line Of Credit Facility [Line Items]
Interest rate spread				0.25%
Five Year Unsecured Revolving Credit Agreement | Maximum | SOFR
Line Of Credit Facility [Line Items]
Interest rate spread				1.25%
$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
Accordion feature				$ 100,000,000
Maximum borrowing capacity post accordion feature				1,000,000,000
Outstanding borrowings				$ 0		0
$900 Million Revolving Credit Facility | Minimum | Revolving Credit Facility | Base Rate
Line Of Credit Facility [Line Items]
Interest rate spread				0.00%
$900 Million Revolving Credit Facility | Minimum | Revolving Credit Facility | SOFR
Line Of Credit Facility [Line Items]
Interest rate spread				0.75%
$900 Million Revolving Credit Facility | Maximum | Revolving Credit Facility | Base Rate
Line Of Credit Facility [Line Items]
Interest rate spread				0.25%
$900 Million Revolving Credit Facility | Maximum | Revolving Credit Facility | 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
Unsecured Senior Term Loan Due 2023 | Unsecured Debt | Line of Credit
Line Of Credit Facility [Line Items]
Debt instrument, face amount		$ 2,020,000,000.00
Floating Rate Senior Notes | Unsecured Debt | Line of Credit
Line Of Credit Facility [Line Items]
Repayment of long-term debt	$ 1,100,000,000