Property, Plant and Equipment (Components of PP&E) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Electric generation, distribution assets and other	$ 28,539	$ 27,282
Accumulated depreciation	(9,528)	(8,939)
Property, Plant and Equipment, Net	19,011	18,343
Electric generation and distribution facilities
Property, Plant and Equipment [Line Items]
Electric generation, distribution assets and other	$ 25,773	24,740
Electric generation and distribution facilities | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	4 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	$ 2,034	1,856
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	63 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Electric generation, distribution assets and other	$ 309	288
Furniture and Fixtures [Member] | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 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	$ 423	$ 398
Other | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	2 years
Other | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	50 years