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Post-Employment and Other Long-Term Employees Benefits - Reconciliation for Plan Assets Measured at Fair Value Using Unobservable Inputs (Level 3) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]    
Plan assets at fair value at beginning of year $ 597  
Foreign currency translation adjustment 0 $ 0
Plan assets at fair value at end of year 718 597
Fair Value, Inputs, Level 3 [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Plan assets at fair value at beginning of year 113 117
Contributions (employer and employee) 14 11
Actual return on plan assets 2 (1)
Net benefit payments 11 9
Settlements   (34)
Transfer in Level 3 10 11
Foreign currency translation adjustment 12  
Plan assets at fair value at end of year $ 162 $ 113