Property, Plant and Equipment (Components of PP&E) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Electric generation, distribution assets and other		$ 28,491	$ 30,459
Accumulated depreciation		(9,449)	(9,962)
Property, Plant and Equipment, Net	[1]	19,042	20,497
Capitalized computer software, net		83	115
Electric generation and distribution facilities
Property, Plant and Equipment [Line Items]
Electric generation, distribution assets and other		$ 25,427	27,488
Electric generation and distribution facilities | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life		5 years
Electric generation and distribution facilities | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life		68 years
Other buildings
Property, Plant and Equipment [Line Items]
Electric generation, distribution assets and other		$ 1,868	1,694
Other buildings | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life		3 years
Other buildings | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life		53 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Electric generation, distribution assets and other		$ 305	307
Furniture and Fixtures [Member] | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life		2 years
Furniture and Fixtures [Member] | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life		31 years
Other
Property, Plant and Equipment [Line Items]
Electric generation, distribution assets and other		$ 891	$ 970
Other | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life		1 year
Other | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life		50 years

[1] (1) Net electric generation and distribution assets and other include unamortized internal-use software costs of $83 million and $115 million as of December 31, 2015 and 2014, respectively.