Property, Plant And Equipment

6 Months Ended

Jun. 30, 2015

Property, Plant And Equipment [Abstract]

Property, Plant And Equipment

(5)   Property, Plant and Equipment:

Property, plant and equipment, net is as follows:

($ in millions)	June 30, 2015		December 31, 2014
Property, plant and equipment	$	17,280	$	16,946
Less:  Accumulated depreciation		(8,848)		(8,380)
Property, plant and equipment, net	$	8,432	$	8,566

Depreciation expense is principally based on the composite group method. Depreciation expense was $247 million and $197 million, and $496million and $403 million, for the three and six months ended June 30, 2015 and 2014, respectively. We adopted new estimated remaining useful lives for certain plant assets as of October 1, 2014, 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. In addition, we commissioned an independent study to determine the estimated useful lives for assets acquired during the Connecticut Acquisition. These new lives were adopted effective October 24, 2014.