Revenues (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2018	Dec. 31, 2017
Revenue, Performance Obligation, Description of Payment Terms		45
Revenue, Remaining Performance Obligation		$ 2,200	$ 2,100
Revenue Recognized on Deferred Revenues		200
Contracted Amounts Receivable from Customers, Current	[1]	2,039
Contracted Amounts Receivable from Customers, in Two Years	[1]	3,829
Contracted Amounts Receivable from Customers, in Three Years	[1]	3,552
Contracted Amounts Receivable from Customers, in Four Years	[1]	3,279
Contracted Amounts Receivable from Customers, in Five Years	[1]	3,054
Contracted Amounts Receivable from Customers, Thereafter	[1]	6,928
Contracted Amounts Receivable from Customers, Total	[1]	22,681
Non-current
Assets Related to Straight Line Site Rental Revenues		1,300
Current
Assets Related to Straight Line Site Rental Revenues		$ 121

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