Revenue Recognition, Disaggregation Of Revenue (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
Revenue from contracts with customers
Revenue from contracts with customers	$ 926	[1]
Transferred over time
Revenue from contracts with customers
Revenue from contracts with customers	708
Transferred over time | Retail service
Revenue from contracts with customers
Revenue from contracts with customers	649
Transferred over time | Inbound roaming
Revenue from contracts with customers
Revenue from contracts with customers	27
Transferred over time | Other service
Revenue from contracts with customers
Revenue from contracts with customers	32
Transferred at point in time
Revenue from contracts with customers
Revenue from contracts with customers	$ 218

[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.