Device Payment Plan Agreement and Wireless Service Receivables - Allowance for Credit Losses (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jan. 01, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 472
Adjusted opening balance, January 1, 2020	472
Ending balance	795
Device payment plan agreement
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	472
Adjusted opening balance, January 1, 2020	795	$ 737
Current period provision for expected credit losses	449
Write-offs charged against the allowance	(415)
Recoveries collected	24
Ending balance	795
Wireless Service Plan Receivables
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	156
Adjusted opening balance, January 1, 2020	234	156
Current period provision for expected credit losses	252
Write-offs charged against the allowance	(208)
Recoveries collected	34
Ending balance	$ 234
Accounting Standards Update 2016-13 | Device payment plan agreement
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Opening balance sheet adjustment related to Topic 326 adoption		265
Accounting Standards Update 2016-13 | Wireless Service Plan Receivables
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Opening balance sheet adjustment related to Topic 326 adoption		$ 0