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Share-Based Compensation and Benefit Plans (Narrative) (Details)
12 Months Ended
Dec. 31, 2020
USD ($)
shares
$ / shares
Dec. 31, 2019
USD ($)
$ / shares
shares
Dec. 31, 2018
USD ($)
$ / shares
May 17, 2018
shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares $ 113.46 $ 98.84 $ 82.81  
Total compensation cost for option and share awards $ 15,300,000 $ 16,800,000 $ 17,800,000  
Total capitalized compensation cost for option and share awards $ 3,400,000   3,000,000.0  
Percentage Of Market Value Per Share At Which Shares Purchased Under Employee Share Purchase Plan 85.00%      
EmployeeSharePurchasePlanMaximumAuthorizedAmountPerParticipant $ 25,000      
Share Awards Held In Employee Trust Shares | shares 1,400,000 1,400,000    
Share Awards Held In Non Qualified Deferred Compensation Plan Shares $ 11,300,000 $ 12,500,000    
Cash Required By Plan Participants Upon Withdrawal 16,500,000 17,300,000    
Defined Contribution Plan, Cost $ 3,400,000 $ 3,100,000 2,900,000  
Employee Share Purchase Program maximum shares available | shares 500,000      
Share Awards Held In Non Qualified Deferred Compensation Plan Shares | shares 900,000 800,000    
Trading Securities Held In Non Qualified Deferred Compensation Plan Value $ 118,500,000 $ 139,300,000    
Options [Member]        
Total intrinsic value of options exercised during the period     2,000,000.0  
Share Awards and Vesting [Member]        
Total unrecognized compensation cost related to unvested options which is expected to be amortized 12,900,000      
Fair value of shares vested $ 18,700,000 $ 25,500,000 $ 24,000,000.0  
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition 2 years      
Maximum [Member] | Share Awards and Vesting [Member]        
Vesting period, years 3 years      
Two Thousand Eighteen Share Incentive Plan [Member]        
Total fungible units to be issued | shares 7,000,000.0     9,700,000
Fungible Units To Full Value Award Conversion Ratio 3.45      
Full Value award in the fungible unit conversion ratio | shares 1.0      
Expiration value of option right or other award | shares 1.0      
Common shares which could be granted pursuant to full value awards | shares 2,000,000.0