Debt - Narrative (Details)						6 Months Ended	9 Months Ended
	Apr. 29, 2021 USD ($)	Apr. 01, 2021 USD ($)	Mar. 31, 2021 USD ($) credit_facility	Mar. 09, 2021 USD ($)	Oct. 01, 2020 USD ($)	Mar. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Sep. 30, 2020 USD ($)
Line Of Credit Facility [Line Items]
Proceeds from issuance of long-term debt							$ 2,797,346,000	$ 999,450,000
Maximum debt-to-total-capitalization ratio							70.00%
Debt-to-total-capitalization ratio							0.50
Minimum
Line Of Credit Facility [Line Items]
Equity-to-total-capitalization ratio							50.00%
Outstanding indebtedness							$ 15,000,000
Maximum
Line Of Credit Facility [Line Items]
Equity-to-total-capitalization ratio							60.00%
Outstanding indebtedness							$ 100,000,000
Revolving Credit Facility
Line Of Credit Facility [Line Items]
Maximum borrowing capacity			$ 2,500,000,000
Number of credit facilities | credit_facility			4
Senior Notes Due 2023
Line Of Credit Facility [Line Items]
Debt instrument, face amount				$ 2,200,000,000
Proceeds net of issuance cost				$ 2,200,000,000
Redemption price (in percent)				100.00%
Unsecured 0.625% Senior Notes, due 2023
Line Of Credit Facility [Line Items]
Debt instrument, face amount				$ 1,100,000,000
Interest rate				0.625%			0.625%
Effective Interest Rate				0.834%
Floating-rate Senior Notes, due 2023
Line Of Credit Facility [Line Items]
Debt instrument, face amount				$ 1,100,000,000
Unsecured 1.50% Senior Notes, due 2031
Line Of Credit Facility [Line Items]
Debt instrument, face amount					$ 600,000,000
Interest rate					1.50%		1.50%
Effective Interest Rate					1.71%
Proceeds from issuance of long-term debt					$ 592,300,000
Five Year Unsecured Revolving Credit Agreement
Line Of Credit Facility [Line Items]
Outstanding commercial paper							$ 0		$ 0
Five Year Unsecured Revolving Credit Agreement | Commercial Paper
Line Of Credit Facility [Line Items]
Maximum borrowing capacity			$ 1,500,000,000			$ 1,500,000,000
Debt agreement term			5 years			5 years
Accordion feature							250,000,000
Maximum borrowing capacity post accordion feature							1,750,000,000
$600 Million Revolving Credit Facility | Revolving Credit Facility
Line Of Credit Facility [Line Items]
Maximum borrowing capacity						$ 600,000,000
Debt agreement term						364 days
$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			$ 1,000,000,000.0
Outstanding borrowings							0
$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
$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
LIBOR | Floating-rate Senior Notes, due 2023
Line Of Credit Facility [Line Items]
Interest rate spread				0.38%
LIBOR | Five Year Unsecured Revolving Credit Agreement | Minimum
Line Of Credit Facility [Line Items]
Interest rate spread			0.00%
LIBOR | Five Year Unsecured Revolving Credit Agreement | Maximum
Line Of Credit Facility [Line Items]
Interest rate spread			0.25%
LIBOR | $900 Million Revolving Credit Facility | Revolving Credit Facility | Minimum
Line Of Credit Facility [Line Items]
Interest rate spread			0.75%
LIBOR | $900 Million Revolving Credit Facility | Revolving Credit Facility | Maximum
Line Of Credit Facility [Line Items]
Interest rate spread			1.25%
Base Rate | Five Year Unsecured Revolving Credit Agreement | Minimum
Line Of Credit Facility [Line Items]
Interest rate spread			0.75%
Base Rate | Five Year Unsecured Revolving Credit Agreement | Maximum
Line Of Credit Facility [Line Items]
Interest rate spread			1.25%
Base Rate | $900 Million Revolving Credit Facility | Revolving Credit Facility | Minimum
Line Of Credit Facility [Line Items]
Interest rate spread			0.00%
Base Rate | $900 Million Revolving Credit Facility | Revolving Credit Facility | Maximum
Line Of Credit Facility [Line Items]
Interest rate spread			0.25%