Wireless Device Payment Plans - Schedule of Device Payment Plan Agreement Receivables (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Device payment plan agreement receivables, gross	$ 17,585	$ 17,770
Unamortized imputed interest	(594)	(821)
Device payment plan agreement receivables, net of unamortized imputed interest	16,991	16,949
Allowance for credit losses	(754)	(848)	$ (715)	$ (688)
Device payment plan agreement receivables, net	16,237	16,101
Account receivable, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Device payment plan agreement receivables, net	11,355	11,064
Other assets
Accounts, Notes, Loans and Financing Receivable [Line Items]
Device payment plan agreement receivables, net	$ 4,882	$ 5,037