Summary of Weighted Average Grant-Date Fair Values And Weighted Average Assumptions Used to Calculate Fair Value of Options Granted (Detail) - $ / shares	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Valuation assumptions:
Risk-free interest rate	0.20%
Expected volatility	35.50%
Employee Stock Option
Valuation assumptions:
Weighted average grant-date fair value	$ 77.82	$ 93.05	$ 141.47
Risk-free interest rate	0.32%	1.97%	2.91%
Expected option life (years)	4 years 2 months 19 days	4 years 1 month 20 days	4 years 15 days
Expected volatility	42.90%	42.30%	42.80%