Revenues (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2018	Dec. 31, 2017
Revenue, Performance Obligation, Description of Payment Terms		45 to 60 days
Revenue, Remaining Performance Obligation, Amount		$ 2,200	$ 2,100
Revenue Recognized on Deferred Revenues		300
Contracted Amounts Receivable from Customers, Current	[1]	1,065
Contracted Amounts Receivable from Customers, in Two Years	[1]	3,935
Contracted Amounts Receivable from Customers, in Three Years	[1]	3,671
Contracted Amounts Receivable from Customers, in Four Years	[1]	3,416
Contracted Amounts Receivable from Customers, in Five Years	[1]	3,193
Contracted Amounts Receivable from Customers, Thereafter	[1]	7,948
Contracted Amounts Receivable from Customers, Total	[1]	23,228
Non-current
Assets Related to Straight Line Site Rental Revenues		1,400
Current
Assets Related to Straight Line Site Rental Revenues		$ 86

[1] Excludes amounts related to network services, as those contracts generally have a duration of one year or less.