Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Schedule of Property, Plant and Equipment [Table Text Block]

Property, plant and equipment includes the following:

	Weighted Average Useful	December 31,
	Lives (in years)	2017		2016
		(in millions)
Transmission	45	$	2,767	$	2,402
Distribution	30	7,178		6,965
Other	15	1,551		1,473
Total		11,496		10,840
Accumulated depreciation		3,633		3,443
Property, plant and equipment, net		$	7,863	$	7,397

Depreciation and Amortization [Table Text Block]

The following table presents depreciation and amortization expense for 2017, 2016 and 2015:

	Year Ended December 31,
	2017		2016		2015
	(in millions)
Depreciation expense	$	354	$	349	$	316
Amortization of securitized regulatory assets	329		455		365
Other amortization	41		34		24
Total depreciation and amortization	$	724	$	838	$	705

Asset Retirement Obligation [Table Text Block]

A reconciliation of the changes in the ARO liability is as follows:

	December 31,
	2017		2016
	(in millions)
Beginning balance	$	33	$	37
Accretion expense	1		1
Revisions in estimates of cash flows	1		(5		)
Ending balance	$	35	$	33