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Share-Based Compensation - Assumptions Used in the Determination of Grant-Date Fair Value of Awards (Details) - TSR Stock Awards [Member] - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Grant date market value of a common share $ 53.26 $ 49.24 $ 40.95
Risk-free interest rate, minimum 1.48% 2.59% 2.32%
Risk-free interest rate, maximum 1.58% 2.66% 2.68%
Dividend yield 2.93% 3.09% 3.52%
Derived vesting period of TSR Restricted Stock and TSR LTIP I units 3 years 6 months 3 years 4 months 24 days 3 years 4 months 24 days
Weighted average expected term of TSR Stock Options and LTIP II units 5 years 10 months 24 days 5 years 9 months 18 days 5 years 7 months 6 days
Minimum [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected volatility 15.82% 19.08% 17.64%
Maximum [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected volatility 16.84% 19.24% 18.02%