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Activity in Allowance for Credit Losses for Device Installment Plan Receivables (Detail)
$ in Millions
12 Months Ended
Dec. 31, 2015
USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]  
Balance at January 1, 2015 $ 76
Bad debt expenses 662
Write-offs (203)
Allowance related to receivables sold (101)
Other 10
Balance at December 31, 2015 $ 444