Device Payment Plan Agreement and Wireless Service Receivables - Schedule of Receivables (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 23,846	$ 26,162
Allowance for credit losses	1,229	0
Accounts receivable, net of allowance	22,617	$ 25,429
Device payment plan agreement
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	11,856
Allowance for credit losses	615
Accounts receivable, net of allowance	11,241
Wireless service
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	5,497
Allowance for credit losses	290
Accounts receivable, net of allowance	5,207
Other receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	6,493
Allowance for credit losses	324
Accounts receivable, net of allowance	$ 6,169