Segment and Related Information - Financial Data for Products and Services (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenue from External Customer [Line Items]
Electric Revenue	$ 5,005,000,000	$ 5,033,000,000	$ 13,120,000,000	$ 12,788,000,000
Financial data for Products and Services
Electric Utilities' Revenues	5,017,000,000	5,049,000,000	13,160,000,000	12,834,000,000
Retail [Member]
Revenue from External Customer [Line Items]
Electric Revenue	4,319,000,000	4,379,000,000	11,237,000,000	11,068,000,000
Wholesale [Member]
Revenue from External Customer [Line Items]
Electric Revenue	520,000,000	497,000,000	1,406,000,000	1,261,000,000
Other [Member]
Revenue from External Customer [Line Items]
Electric Revenue	$ 166,000,000	$ 157,000,000	$ 477,000,000	$ 459,000,000