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Share-Based Compensation and Benefit Plans (Narrative) (Details)
12 Months Ended
Dec. 31, 2018
USD ($)
shares
Dec. 31, 2017
USD ($)
shares
Dec. 31, 2016
USD ($)
May 17, 2018
shares
Granted, Options Outstanding | shares 9,994      
Total compensation cost for option and share awards $ 17,800,000 $ 18,800,000 $ 21,300,000  
Total capitalized compensation cost for option and share awards $ 3,000,000 $ 3,800,000 3,800,000  
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 1,700,000 1,700,000    
Share Awards Held In Non Qualified Deferred Compensation Plan Shares $ 14,900,000 $ 26,700,000    
Cash Required By Plan Participants Upon Withdrawal $ 21,200,000 $ 22,300,000    
Share Awards Held In Non Qualified Deferred Compensation Plan Shares | shares 700,000 1,000,000    
Trading Securities Held In Non Qualified Deferred Compensation Plan Value $ 129,800,000 $ 93,600,000    
Defined Contribution Plan, Cost $ 2,900,000 $ 2,700,000 2,700,000  
Number of shares diversified | shares 429,000 261,000    
Employee Share Purchase Program maximum shares available | shares 500,000      
Options [Member]        
Total intrinsic value of options exercised during the period $ 2,000,000 $ 2,200,000 8,900,000  
Share Awards and Vesting [Member]        
Total unrecognized compensation cost related to unvested options which is expected to be amortized 15,400,000      
Fair value of shares vested $ 24,000,000 $ 23,100,000 $ 27,200,000  
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition 2 years      
Maximum [Member] | Share Awards and Vesting [Member]        
Vesting period, years 5 years      
Two Thousand Eighteen Share Incentive Plan [Member]        
Total fungible units to be issued | shares 8,200,000     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 2,400,000