Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2015

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

Property, plant and equipment includes the following:

	Weighted Average Useful Lives	December 31,
	(Years)	2015		2014
		(in millions)
Natural Gas Distribution	32	$	5,762	$	5,235
Energy Services	27	86		84
Other property	10	50		45
Total		5,898		5,364
Accumulated depreciation and amortization:
Natural Gas Distribution		1,575		1,493
Energy Services		34		31
Other property		31		30
Total accumulated depreciation and amortization		1,640		1,554
Property, plant and equipment, net		$	4,258	$	3,810

Depreciation And Amortization [Table Text Block]

The following table presents depreciation and amortization expense for 2015, 2014 and 2013:

	Year Ended December 31,
	2015		2014		2013
	(in millions)
Depreciation expense	$	211	$	195	$	218
Amortization expense	16		11		12
Total depreciation and amortization expense	$	227	$	206	$	230

Asset Retirement Obligations

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

	December 31,
	2015		2014
	(in millions)
Beginning balance	$	139	$	101
Accretion expense	5		4
Revisions in estimates of cash flows	12		34
Ending balance	$	156	$	139