Device Payment Plan Agreement and Wireless Service Receivables - Schedule of Credit Quality Indicators (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Device payment plan agreement receivables, at amortized cost	$ 18,991	$ 17,959
Device payment plan agreement
Financing Receivable, Credit Quality Indicator [Line Items]
2021	11,826
2020	6,257
Prior to 2020	543
Device payment plan agreement receivables, at amortized cost	18,626
Device payment plan agreement | New customers
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,846
2020	869
Prior to 2020	75
Device payment plan agreement receivables, at amortized cost	2,790
Device payment plan agreement | Existing customers
Financing Receivable, Credit Quality Indicator [Line Items]
2021	9,980
2020	5,388
Prior to 2020	468
Device payment plan agreement receivables, at amortized cost	$ 15,836