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Schedule II Valuation and Qualifying Accounts (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of period $ 8,077    
Deductions (20,480)    
Balance at end of period 6,886 $ 8,077  
Allowance For Doubtful Accounts [Member]      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of period 232 191 $ 146
Charged to costs and expenses 13 12 5
Charged to other accounts (9) 51 61
Deductions (4) (22) (21)
Balance at end of period 232 232 191
Valuation Allowance in Tax Carryforward Losses And Deductions [Member]      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of period 1,504 1,690 760
Charged to costs and expenses 407 173 135
Charged to other accounts 5 390 1,137
Deductions (283) (749) (342)
Balance at end of period $ 1,633 $ 1,504 $ 1,690