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Supplementary Information - Change in Allowance for Doubtful Accounts (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Segment Reporting [Abstract]      
Balance at beginning of year $ 241 $ 397 $ 333
Additions 15 7 123
Amounts written off (7) (163) (59)
Balance at end of year $ 249 $ 241 $ 397