Share-Based Payments - Schedule of Valuation Assumptions (Detail) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
|
| Total Shareholder Return Units (TSRUs) [Member] | |||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Expected dividend yield | 4.36% | 3.27% | 3.73% |
| Risk-free interest rate | 1.15% | 2.55% | 2.60% |
| Expected stock price volatility | 20.99% | 18.34% | 20.00% |
| Contractual term/expected term | 5 years 1 month 13 days | 5 years 1 month 17 days | 5 years 1 month 13 days |
| Share-based Payment Arrangement, Option [Member] | |||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Expected dividend yield | 4.36% | 3.27% | 3.73% |
| Risk-free interest rate | 1.25% | 2.66% | 2.85% |
| Expected stock price volatility | 20.97% | 18.34% | 20.02% |
| Contractual term/expected term | 6 years 9 months | 6 years 9 months | 6 years 9 months |