Short-Term Borrowings - Narrative (Details) - USD ($)	1 Months Ended
	Jan. 31, 2020	Sep. 30, 2019	Sep. 30, 2018	Feb. 01, 2019	Jan. 31, 2019
Short-term Debt [Line Items]
Unsecured notes, issued	$ 3,000,000,000.0
Outstanding borrowings under term loan	$ 1,941,000,000			$ 722,000,000
Weighted average interest rate of short-term borrowings	2.14%			2.81%
Amount outstanding under the commercial paper program	$ 941,000,000			$ 722,000,000
The Term Loan [Member]
Short-term Debt [Line Items]
Unsecured notes, issued	$ 1,000,000,000.0
Debt instrument term	364 days
Outstanding borrowings under term loan	$ 1,000,000,000.0
Weighted average interest rate of short-term borrowings	2.29%
The Term Loan [Member] | Base Rate
Short-term Debt [Line Items]
Basis spread on variable rate	0.00%
The Term Loan [Member] | Eurocurrency
Short-term Debt [Line Items]
Basis spread on variable rate	0.625%
2019 Credit Agreement [Member] | Revolving Credit Facility
Short-term Debt [Line Items]
Debt instrument term		364 days
Maximum borrowing capacity		$ 250,000,000
Second Amended And Restated Credit Agreement [Member]
Short-term Debt [Line Items]
Amount outstanding under the credit facility	$ 0
Second Amended And Restated Credit Agreement [Member] | Revolving Credit Facility
Short-term Debt [Line Items]
Debt instrument term			5 years
Maximum borrowing capacity			$ 1,750,000,000		$ 1,980,000,000
Increase in borrowing capacity					230,000,000
Optional increase in borrowing capacity					$ 270,000,000
2018 Credit Agreement [Member] | Revolving Credit Facility
Short-term Debt [Line Items]
Debt instrument term			364 days
Maximum borrowing capacity			$ 250,000,000
Commercial Paper [Member]
Short-term Debt [Line Items]
Weighted average interest rate of short-term borrowings	2.10%			2.81%