Revenues and Contract Costs - Schedule of Receivables from Contracts with Customers (Details) - USD ($) $ in Millions	Jun. 30, 2019	Jan. 01, 2019	Jun. 30, 2018	Jan. 01, 2018
Revenue from Contract with Customer [Abstract]
Receivables	$ 12,173	$ 12,104	$ 11,412	$ 12,073
Device payment plan agreement receivables	$ 10,053	$ 8,940	$ 5,258	$ 1,461