Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2012

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

Property, plant and equipment includes the following:

	Weighted Average Useful Lives	December 31,
	(Years)	2011		2012
		(in millions)
Natural Gas Distribution	32	$	3,959	$	4,321
Competitive Natural Gas Sales and Services	26	76		80
Interstate Pipelines	56	2,675		2,803
Field Services	42	1,754		2,359
Other property	12	55		52
Total		8,519		9,615
Accumulated depreciation and amortization:
Natural Gas Distribution		1,069		1,194
Competitive Natural Gas Sales and Services		20		25
Interstate Pipelines		302		355
Field Services		72		118
Other property		26		22
Total accumulated depreciation and amortization		1,489		1,714
Property, plant and equipment, net		$	7,030	$	7,901

Depreciation And Amortization [Table Text Block]

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

	Year Ended December 31,
	2010		2011		2012
	(in millions)
Depreciation expense	$	232	$	244	$	267
Amortization expense	16		18		18
Total depreciation and amortization expense	$	248	$	262	$	285

Asset Retirement Obligations

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

	December 31,
	2011		2012
Beginning balance	$	58	$	132
Accretion expense	3		6
Revisions in estimates of cash flows	71		(3		)
Ending balance	$	132	$	135