Device Payment Plan Agreement and Wireless Service Receivables - Schedule of Device Payment Plan Agreement Receivables (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Device payment plan agreement receivables, gross	$ 16,597	$ 19,493
Unamortized imputed interest	(424)	(454)
Device payment plan agreement receivables, at amortized cost	16,173	19,039
Allowance	(833)	(472)
Device payment plan agreement receivables, net	15,340	18,567
Account receivable, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Device payment plan agreement receivables, net	11,241	13,045
Other assets
Accounts, Notes, Loans and Financing Receivable [Line Items]
Device payment plan agreement receivables, net	$ 4,099	$ 5,522