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Common Stock - Summary of Information and Changes in Stock Options with Regard to Stock Option Plans (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Number of shares under stock option, Beginning of the year 22,472,047 17,439,060 15,430,307
Number of Shares Granted 1,610,599 6,961,041 3,672,411
Number of Shares Forfeited (1,318,380) (1,482,531) (1,517,065)
Number of Shares Exercised (1,754,758) (445,523) (146,593)
Number of shares under stock option, End of the year 21,009,508 22,472,047 17,439,060
Number of stock options, Exercisable 15,223,029 14,309,944 9,828,897
Weighted Average Exercise Price, Beginning of year $ 48.99 $ 54.08 $ 59.50
Weighted Average Exercise Price, Stock Options Granted 35.09 36.51 28.26
Weighted Average Exercise Price, Stock Options Forfeited 57.56 55.22 49.95
Weighted Average Exercise Price, Stock Options Exercised 44.12 29.83 28.53
Weighted Average Exercise Price, End of the year 48.88 48.99 54.08
Weighted Average Exercise Price, Stock Options, Exercisable $ 54.13 $ 55.00 $ 61.56
Weighted Average Remaining Contractual Term, Outstanding 6 years 4 days 6 years 7 months 28 days  
Weighted Average Remaining Contractual Term, Exercisable 5 years 2 months 27 days    
Stock Options Aggregate Intrinsic Value, Beginning $ 34,186,368    
Stock Options Aggregate Intrinsic Value, Ending 458,576 $ 34,186,368  
Stock Options Average Aggregate Intrinsic Value, Exercisable $ 458,576