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Fair Value Measurement - Summary of Fair Value of Financial Liabilities Measured Using Level 3 Inputs (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value at the beginning of the period $ (448) $ (497)
Transfer into Level 3- equity securities 179  
Revaluation of equity securities 80  
Revaluation of debt securities (2) 2
Reclassification to Level 2- equity securities (259)  
Fair value at the end of the period (258) (448)
Actavis Generics [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Actavis Generics transaction 156 92
Eagle Transaction [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Adjustments to provisions for contingent consideration (75) (151)
Settlement of contingent consideration $ 111 $ 106