Revenue Recognition, Accounts Receivable (Details) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Accounts receivable
Customer and agents		$ 809	$ 775
Roaming		25	26
Other		40	$ 41
Accounts receivable from contract with customer
Accounts receivable
Customer and agents		809
Roaming		25
Other		32
Total	[1]	$ 866

[1] These amounts do not include accounts receivable related to revenues outside the scope of ASU 2014-09; therefore, accounts receivable line items presented in this table will not agree to amounts presented in the Consolidated Balance Sheet.