Revenue Recognition, Disaggregation Of Revenue (Details) - USD ($) $ in Millions		3 Months Ended	6 Months Ended
		Jun. 30, 2018	Jun. 30, 2018
Revenue from contracts with customers
Revenue from contracts with customers	[1]	$ 957	$ 1,882
Transferred over time
Revenue from contracts with customers
Revenue from contracts with customers		724	1,432
Transferred over time | Retail service
Revenue from contracts with customers
Revenue from contracts with customers		652	1,301
Transferred over time | Inbound roaming
Revenue from contracts with customers
Revenue from contracts with customers		39	66
Transferred over time | Other service
Revenue from contracts with customers
Revenue from contracts with customers		33	65
Transferred at point in time
Revenue from contracts with customers
Revenue from contracts with customers		$ 233	$ 450

[1] These amounts do not include revenues outside the scope of ASU 2014-09; therefore, revenue line items in this table will not agree to amounts presented in the Consolidated Statement of Operations.