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Commitments - Summary of Contractual Obligations (Parenthetical) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Disclosure of Detailed Information About Borrowings [Line Items]    
Future minimum lease payments $ 1,323  
Estimated annual benefit payment period next 10 years next 10 years
1-3 years [Member]    
Disclosure of Detailed Information About Borrowings [Line Items]    
Future minimum lease payments $ 436  
3-5 Years [Member]    
Disclosure of Detailed Information About Borrowings [Line Items]    
Future minimum lease payments $ 242