Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

Schedule of net property, plant and equipment

Net property, plant and equipment is composed of the following:

	Depreciable Lives	As of December 31,
		2018			2017
		(Dollars in millions)
Land	N/A	$	871		883
Fiber, conduit and other outside plant(1)	15-45 years	23,936			22,798
Central office and other network electronics(2)	3-10 years	18,736			18,538
Support assets(3)	3-30 years	8,020			7,586
Construction in progress(4)	N/A	1,704			1,399
Gross property, plant and equipment		53,267			51,204
Accumulated depreciation		(26,859		)	(24,352	)
Net property, plant and equipment		$	26,408		26,852

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(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, cable landing stations, data centers, 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.

Schedule of changes to asset retirement obligations

The following table provides asset retirement obligation activity:

	Years Ended December 31,
	2018			2017		2016
	(Dollars in millions)
Balance at beginning of year	$	115		95		91
Accretion expense	10			6		6
Liabilities assumed in acquisition of Level 3(1)	58			45		—
Liabilities settled	(14		)	(3	)	(2	)
Liabilities transferred to Cyxtera	—			(20	)	—
Change in estimate	21			(8	)	—
Balance at end of year	$	190		115		95

(1) The liabilities assumed during 2018 relate to purchase price adjustments during the year.