Property, Plant And Equipment

12 Months Ended

Dec. 31, 2015

Property, Plant And Equipment [Abstract]

Property, Plant And Equipment

(5)   Property, Plant and Equipment:

Property, plant and equipment, net at December 31, 2015 and 2014 are as follows:

($ in millions)	Estimated Useful Lives	2015		2014
Land	N/A	$	151	$	147
Buildings and leasehold improvements	41 years		1,327		1,326
General support	5 to 17 years		1,146		1,037
Central office/electronic circuit equipment	5 to 18 years		6,244		5,934
Poles	30 years		712		672
Cable and wire	15 to 25 years		7,280		6,973
Conduit	55 years		515		509
Other	12 to 25 years		47		47
Construction work in progress			379		301
Property, plant and equipment			17,801		16,946
Less: Accumulated depreciation			(9,308)		(8,380)
Property, plant and equipment, net		$	8,493	$	8,566

Depreciation expense is principally based on the composite group method.  Depreciation expense was $983million,  $835 million and $841 million for the years ended December 31, 2015, 2014 and 2013, respectively. We adopted new estimated remaining useful lives for certain plant assets as of October 1, 2015, as a result of our annual independent study of the estimated remaining useful lives of our plant assets, with an insignificant impact to depreciation expense.