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Stock-Based Compensation Plans (Narrative) (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Mar. 26, 2012
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares available for issuance   126,348    
Fair value of shares vested   $ 4.8 $ 5.6 $ 4.4
Intrinsic value of restricted stock units exercised   $ 0.5 $ 6.9 $ 78.7
Weighted average recognition period   1 year 10 months    
Restricted Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Weighted average fair value of shares granted   $ 317.87 $ 200.79 $ 196.96
Restricted Stock Units (RSUs) [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Weighted average fair value of shares granted   $ 363.11 $ 206.45 $ 181.04
Restricted stock units converted to common stock, shares   1,439    
Ten Year Vesting [Member] | Restricted Stock Units (RSUs) [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   10 years    
Five Year Vesting [Member] | Restricted Stock Units (RSUs) [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   5 years    
Three Year Vesting [Member] | Restricted Stock Units (RSUs) [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   4 years    
Minimum [Member] | Fifteen Year Vesting [Member] | Restricted Stock [Member] | Chief Executive Officer [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   15 years    
Minimum [Member] | Three Year Vesting [Member] | Restricted Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period   3 years    
Incentive Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of additional shares authorized for issuance 500,000      
Total authorized shares for plan issuance   2,000,000