Revenue Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue recognized on performance obligations	$ 202	$ 570
Revenue, Remaining Performance Obligation, Amount	$ 940	$ 940
Network Services
Disaggregation of Revenue [Line Items]
Expected timing of satisfaction for performance obligation	10 years	10 years
Accounts receivable
Disaggregation of Revenue [Line Items]
Contract assets	$ 2,156	$ 2,156	$ 1,873
Other current assets
Disaggregation of Revenue [Line Items]
Contract assets	36	36
Other Assets
Disaggregation of Revenue [Line Items]
Contract assets	77	77
Other current liabilities
Disaggregation of Revenue [Line Items]
Deferred revenue	260	260	230
Other liabilities
Disaggregation of Revenue [Line Items]
Deferred revenue	$ 111	$ 111	$ 17