Credit Agreements - Schedule of Debt Instruments (Parenthetical) (Details)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Feb. 26, 2020	May 31, 2018	Mar. 31, 2015
4.600% Senior Notes Due May 2028
Debt Instrument [Line Items]
Debt instrument interest rate, stated percentage	4.60%	4.60%		4.60%
Maturity month and year	2028-05	2028-05
3.100% Senior Notes due March 2030
Debt Instrument [Line Items]
Debt instrument interest rate, stated percentage	3.10%		3.10%
Maturity month and year	2030-03
5.375% Senior Notes due March 2025
Debt Instrument [Line Items]
Debt instrument interest rate, stated percentage		5.375%			5.375%
Maturity month and year		2025-03