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Supplementary Information - Change in Allowance for Doubtful Accounts (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Segment Reporting [Abstract]      
Balance at beginning of year $ 249 $ 241 $ 397
Additions 5 15 7
Amounts written off 1 (7) (163)
Balance at end of year $ 255 $ 249 $ 241