Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, plant and equipment
Gross property, plant and equipment	$ 15,916	$ 15,028
Accumulated depreciation	(7,746)	(6,951)
Net property, plant and equipment	8,170	8,077
Depreciation expense	831	855	$ 912
Land
Property, plant and equipment
Gross property, plant and equipment	332	332
Fiber, conduit and other outside plant
Property, plant and equipment
Gross property, plant and equipment	$ 7,735	7,171
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	$ 4,641	4,361
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	$ 2,670	2,656
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	$ 538	$ 508