Segment and Related Information - Financial Data for Products and Services (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Revenue from External Customer [Line Items]
Electric Revenue	$ 4,454,000,000	$ 4,230,000,000	$ 9,081,000,000	$ 8,116,000,000
Financial data for Products and Services
Electric Utilities' Revenues	4,467,000,000	4,246,000,000	9,111,000,000	8,143,000,000
Retail [Member]
Revenue from External Customer [Line Items]
Electric Revenue	3,770,000,000	3,620,000,000	7,628,000,000	6,918,000,000
Wholesale [Member]
Revenue from External Customer [Line Items]
Electric Revenue	515,000,000	454,000,000	1,119,000,000	886,000,000
Other [Member]
Revenue from External Customer [Line Items]
Electric Revenue	$ 169,000,000	$ 156,000,000	$ 334,000,000	$ 312,000,000