Share-based Compensation - Assumptions Used to Estimate the Fair Value of Each Stock Option on the Date of Grant Using a Black-Scholes Option Pricing Model (Detail) - Stock Option - $ / shares	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	4 years 1 month 9 days	4 years 25 days	4 years 10 days
Risk-free rate of return	1.10%	0.30%	1.60%
Expected volatility	27.10%	25.10%	18.70%
Expected dividend yield	0.70%	0.60%	0.70%
Fair value per performance-based share granted (in dollars per share)	$ 43.16	$ 39.51	$ 29.37