Property, Plant and Equipment (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, plant and equipment
Gross property, plant and equipment		$ 15,028	$ 14,316
Accumulated depreciation		(6,951)	(6,392)
Net property, plant and equipment		8,077	7,924
Depreciation expense		855	912	$ 924
Land
Property, plant and equipment
Gross property, plant and equipment		332	333
Fiber, conduit and other outside plant
Property, plant and equipment
Gross property, plant and equipment	[1]	$ 7,171	6,639
Fiber, conduit and other outside plant | Minimum
Property, plant and equipment
Depreciable lives		15 years
Fiber, conduit and other outside plant | Maximum
Property, plant and equipment
Depreciable lives		45 years
Central office and other network electronics
Property, plant and equipment
Gross property, plant and equipment	[2]	$ 4,361	4,250
Central office and other network electronics | Minimum
Property, plant and equipment
Depreciable lives		7 years
Central office and other network electronics | Maximum
Property, plant and equipment
Depreciable lives		10 years
Support assets
Property, plant and equipment
Gross property, plant and equipment	[3]	$ 2,656	2,620
Support assets | Minimum
Property, plant and equipment
Depreciable lives		5 years
Support assets | Maximum
Property, plant and equipment
Depreciable lives		30 years
Construction in progress
Property, plant and equipment
Gross property, plant and equipment	[4]	$ 508	$ 474

[1] Fiber, conduit and other outside plant consists of fiber and metallic cable, conduit, poles and other supporting structures.

[2] Central office and other network electronics consists of circuit and packet switches, routers, transmission electronics and electronics providing service to customers.

[3] Support assets consist of buildings, computers and other administrative and support equipment.

[4] Construction in progress includes inventory held for construction and property of the aforementioned categories that has not been placed in service as it is still under construction.