Segment and Related Information - Financial Data for Products and Services (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	$ 4,324	$ 4,454	$ 8,496	$ 9,081
Retail [Member]
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	3,714	3,770	7,256	7,628
Wholesale [Member]
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	448	515	915	1,119
Other [Member]
Revenue from External Customer [Line Items]
Electric Utilities' Revenues	$ 162	$ 169	$ 325	$ 334