Share-based Compensation - Fair Value Assumptions (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free rate of return, minimum	1.66%	2.61%	1.83%
Risk-free rate of return, maximum	2.23%	2.96%	2.22%
Expected volatility, minimum	18.18%	17.82%	18.13%
Expected volatility, maximum	19.15%	18.44%	18.70%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yields	1.76%	1.71%	1.63%
Expected award life (years)	4 years 5 months 27 days	4 years 5 months 23 days	4 years 5 months 23 days
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yields	1.83%	1.87%	1.72%
Expected award life (years)	4 years 6 months	4 years 5 months 27 days	4 years 5 months 27 days