Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2012

Property, Plant and Equipment [Abstract]

Schedule of Property, Plant and Equipment

Property, plant and equipment includes the following:

	Weighted Average Useful	December 31,
	Lives (Years)	2011		2012
		(in millions)
Transmission	41	$	1,720	$	1,851
Distribution	29	5,327		5,548
Other	15	780		805
Total		7,827		8,204
Accumulated depreciation		2,784		2,839
Property, plant and equipment, net		$	5,043	$	5,365

Depreciation and Amortization

The following table presents depreciation and amortization expense for 2010, 2011 and 2012:

	Year Ended December 31,
	2010		2011		2012
	(in millions)
Depreciation expense	$	273	$	257	$	265
Amortization of securitized regulatory assets	289		308		442
Other amortization	20		22		22
Total depreciation and amortization	$	582	$	587	$	729

Asset Retirement Obligation

A reconciliation of the changes in the asset retirement obligation (ARO) liability is as follows (in millions):

	December 31,
	2011			2012
Beginning balance	$	26		$	23
Accretion expense	1			1
Revisions in estimates of cash flows	(4		)	5
Ending balance	$	23		$	29