Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment, Net, by Type [Abstract]
Total	$ 10,840	$ 10,142
Accumulated depreciation	3,443	3,209
Property, plant and equipment, net	7,397	6,933
Depreciation, Depletion and Amortization [Abstract]
Depreciation expense	349	316	$ 295
Amortization of securitized regulatory assets	455	365	441
Other amortization	34	24	32
Total depreciation and amortization	838	705	768
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	37	36
Accretion expense	1	1
Revisions in estimates of cash flows	(5)	0
Ending balance	33	37	$ 36
Transmission [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total	2,402	2,196
Distribution [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total	6,965	6,556
Other [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total	$ 1,473	$ 1,390
Weighted Average [Member] | Transmission [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	44 years
Weighted Average [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	31 years
Weighted Average [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	14 years