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Activity in Allowance for Credit Losses for Device Payment Plan Agreement Receivables (Detail) - USD ($)
$ in Millions
6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]    
Balance at January 1, 2017 $ 688 $ 444
Bad debt expense 315 310
Write-offs (288) (210)
Allowance related to receivables sold   28
Other   6
Balance at June 30, 2017 $ 715 $ 578