Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, plant and equipment
Gross property, plant and equipment	$ 14,316	$ 13,247
Accumulated depreciation	(6,392)	(5,602)
Net property, plant and equipment	7,924	7,645
Depreciation expense	912	924	$ 986
Land
Property, plant and equipment
Gross property, plant and equipment	333	348
Fiber, conduit and other outside plant(1)
Property, plant and equipment
Gross property, plant and equipment	$ 6,639	5,980
Fiber, conduit and other outside plant(1) | Minimum
Property, plant and equipment
Depreciable lives	15 years
Fiber, conduit and other outside plant(1) | Maximum
Property, plant and equipment
Depreciable lives	45 years
Central office and other network electronics(2)
Property, plant and equipment
Gross property, plant and equipment	$ 4,250	3,855
Central office and other network electronics(2) | Minimum
Property, plant and equipment
Depreciable lives	4 years
Central office and other network electronics(2) | Maximum
Property, plant and equipment
Depreciable lives	10 years
Support assets(3)
Property, plant and equipment
Gross property, plant and equipment	$ 2,620	2,633
Support assets(3) | Minimum
Property, plant and equipment
Depreciable lives	5 years
Support assets(3) | Maximum
Property, plant and equipment
Depreciable lives	30 years
Construction in progress(4)
Property, plant and equipment
Gross property, plant and equipment	$ 474	$ 431