Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment, Net, by Type [Abstract]
Total	$ 10,142	$ 9,393
Accumulated depreciation	3,209	3,050
Property, plant and equipment, net	6,933	6,343
Depreciation, Depletion and Amortization [Abstract]
Depreciation expense	316	295	$ 280
Amortization of securitized regulatory assets	365	441	383
Other amortization	24	32	22
Total depreciation and amortization	705	768	685
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	36	33
Accretion expense	1	1
Revisions in estimates of cash flows	0	2
Ending balance	37	36	$ 33
Transmission [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total	2,196	2,057
Distribution [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total	6,556	6,170
Other [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total	$ 1,390	$ 1,166
Weighted Average [Member] | Transmission [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	41 years
Weighted Average [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	30 years
Weighted Average [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	16 years