Revenues (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Revenue, Performance Obligation, Description of Payment Terms		45
Revenue, Remaining Performance Obligation			$ 2,100
Revenue Recognized on Deferred Revenues		$ 100
Contracted Amounts Receivable from Customers, Current	[1]	3,007
Contracted Amounts Receivable from Customers, in Two Years	[1]	3,755
Contracted Amounts Receivable from Customers, in Three Years	[1]	3,476
Contracted Amounts Receivable from Customers, in Four Years	[1]	3,195
Contracted Amounts Receivable from Customers, in Five Years	[1]	2,956
Contracted Amounts Receivable from Customers, Thereafter	[1]	5,900
Contracted Amounts Receivable from Customers, Total	[1]	22,289
Non-current
Assets Related to Straight Line Site Rental Revenues		1,300
Current
Assets Related to Straight Line Site Rental Revenues		$ 100

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