Device Payment Plan Agreement and Wireless Service Receivables - Balance and Aging of Receivables (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Device payment plan agreement receivables, at amortized cost	$ 18,320	$ 19,493
Device Payment Plan Agreement Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Device payment plan agreement receivables, at amortized cost	17,895
Device Payment Plan Agreement Receivables | Unbilled
Accounts, Notes, Loans and Financing Receivable [Line Items]
Device payment plan agreement receivables, current	16,636
Device Payment Plan Agreement Receivables | Billed
Accounts, Notes, Loans and Financing Receivable [Line Items]
Device payment plan agreement receivables, current	965
Device payment plan agreement receivables, past due	$ 294