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Accounts Receivable - Additional Information (Detail) - USD ($)
6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Accounts Receivable, Net, Current [Abstract]      
Allowance for doubtful accounts receivables $ 83,000,000   $ 35,000,000
Bad debt expense $ 48,000,000 $ 0