Revenues and Contract Costs - Schedule of Receivables from Contracts with Customers (Details) - USD ($) $ in Millions	Jun. 30, 2020	Jan. 01, 2020	Jun. 30, 2019	Jan. 01, 2019
Revenue from Contract with Customer [Abstract]
Receivables	$ 10,967	$ 12,078	$ 12,173	$ 12,104
Device payment plan agreement receivables	$ 10,047	$ 11,741	$ 10,053	$ 8,940