Property, Plant and Equipment - Net Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment, Net [Abstract]
Gross property, plant and equipment	$ 16,656	$ 15,916
Accumulated depreciation	(8,347)	(7,746)
Net property, plant and equipment	8,309	8,170
Land
Property, Plant and Equipment, Net [Abstract]
Gross property, plant and equipment	332	332
Fiber, conduit and other outside plant
Property, Plant and Equipment, Net [Abstract]
Gross property, plant and equipment	$ 8,270	7,735
Fiber, conduit and other outside plant | Minimum
Property, Plant and Equipment [Line Items]
Depreciable lives	15 years
Fiber, conduit and other outside plant | Maximum
Property, Plant and Equipment [Line Items]
Depreciable lives	45 years
Central office and other network electronics
Property, Plant and Equipment, Net [Abstract]
Gross property, plant and equipment	$ 4,964	4,641
Central office and other network electronics | Minimum
Property, Plant and Equipment [Line Items]
Depreciable lives	7 years
Central office and other network electronics | Maximum
Property, Plant and Equipment [Line Items]
Depreciable lives	10 years
Support assets
Property, Plant and Equipment, Net [Abstract]
Gross property, plant and equipment	$ 2,679	2,670
Support assets | Minimum
Property, Plant and Equipment [Line Items]
Depreciable lives	3 years
Support assets | Maximum
Property, Plant and Equipment [Line Items]
Depreciable lives	30 years
Construction in progress
Property, Plant and Equipment, Net [Abstract]
Gross property, plant and equipment	$ 411	$ 538