Device Payment Plan Agreement and Wireless Service Receivables - Schedule of Credit Quality Indicators (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Device payment plan agreement receivables, at amortized cost	$ 18,320	$ 19,493
Device Payment Plan Agreement Receivables
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,280
2019	11,788
2018	2,752
Prior to 2018	75
Device payment plan agreement receivables, at amortized cost	17,895
Device Payment Plan Agreement Receivables | New customers
Financing Receivable, Credit Quality Indicator [Line Items]
2020	560
2019	1,930
2018	348
Prior to 2018	44
Device payment plan agreement receivables, at amortized cost	2,882
Device Payment Plan Agreement Receivables | Existing customers
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,720
2019	9,858
2018	2,404
Prior to 2018	31
Device payment plan agreement receivables, at amortized cost	$ 15,013