v3.8.0.1
Share-Based Payments (Summary of the Company's Employee Restricted Stock Shares, Restricted Stock Units and Performance Shares (Details) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Minimum      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Number of shares to be awarded at the end of each performance period 0.00%    
Maximum      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Number of shares to be awarded at the end of each performance period 125.00%    
Employee restricted stock units      
Restricted Awards      
Restricted (in shares) 4,979,707    
Granted (in shares) 1,540,848    
Forfeited (in shares) (125,209)    
Released (in shares) (1,253,305)    
Restricted (in shares) 5,142,041 4,979,707  
Weighted Average Grant Date Fair Value      
Restricted (in dollars per share) $ 73.77    
Granted (in dollars per share) 110.39 $ 64.12 $ 78.4
Forfeited (in dollars per share) 83.34    
Released (in dollars per share) 84.08    
Restricted (in dollars per share) $ 82.00 $ 73.77  
Employee performance shares and performance units      
Restricted Awards      
Restricted (in shares) 1,663,673    
Granted (in shares) 601,179    
Forfeited (in shares) (9,610)    
Performance adjustment (in shares) 105,829    
Released (in shares) (540,739)    
Restricted (in shares) 1,820,332 1,663,673  
Weighted Average Grant Date Fair Value      
Restricted (in dollars per share) $ 104.06    
Granted (in dollars per share) 114.98 $ 104.06 $ 81.41
Forfeited (in dollars per share) 109.21    
Performance adjustment (in dollars per share) 110.45    
Released (in dollars per share) 110.45    
Restricted (in dollars per share) $ 114.98 $ 104.06