Device Payment Plan Agreement and Wireless Service Receivables - Allowance for Credit Losses (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Jan. 01, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 472
Adjusted opening balance, January 1, 2020	472
Ending balance	830
Device Payment Plan Agreement Receivables
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	472
Adjusted opening balance, January 1, 2020	830	$ 737
Current period provision for expected credit losses	312
Write-offs charged against the allowance	(229)
Recoveries collected	10
Ending balance	830
Wireless Service Plan Receivables
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	156
Adjusted opening balance, January 1, 2020	228	156
Current period provision for expected credit losses	170
Write-offs charged against the allowance	(113)
Recoveries collected	15
Ending balance	$ 228
Accounting Standards Update 2016-13 | Device Payment Plan Agreement Receivables
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