Property, Plant and Equipment, Net (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Utility plant in-service:
Common general	$ 235	$ 212
Utility plant in-service	3,822	3,764
Accumulated depreciation and amortization	(1,334)	(1,301)
Utility plant in-service, net	2,488	2,463
Construction work-in-progress	99	89
Property, plant and equipment, net	2,587	2,552
Electric Plant [Member]
Utility plant in-service:
Generation	1,054	1,070
Distribution	1,314	1,289
Transmission	718	685
Intangible plant	127	138
Gas Plant [Member]
Utility plant in-service:
Distribution	361	357
Intangible plant	$ 13	$ 13