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Schedule II Valuation and Qualifying Accounts (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of period $ 6,886 $ 8,077  
Deductions (17,605) (20,480)  
Balance at end of period 6,246 6,886 $ 8,077
Allowance For Doubtful Accounts [Member]      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of period 232 232 191
Charged to costs and expenses (16) 13 12
Charged to other accounts   (9) 51
Deductions (7) (4) (22)
Balance at end of period 209 232 232
Valuation Allowance in Tax Carryforward Losses And Deductions [Member]      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of period 1,633 1,504 1,690
Charged to costs and expenses 555 407 173
Charged to other accounts   5 390
Deductions (214) (283) (749)
Balance at end of period $ 1,974 $ 1,633 $ 1,504