Segment and Related Information - Financial Data for Products and Services (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	$ 5,327	$ 5,005	$ 14,408	$ 13,120
Retail [Member]
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	4,558	4,319	12,186	11,237
Wholesale [Member]
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	600	520	1,719	1,406
Other [Member]
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	$ 169	$ 166	$ 503	$ 477