Property, Plant and Equipment (Components of PP&E) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Electric generation, distribution assets and other	$ 24,119	$ 24,911
Accumulated depreciation	(7,942)	(7,919)
Property, Plant and Equipment, Net	16,177	16,992
Property Plant And Equipment Net Of Accumulated Depreciation Mortgaged Pledged Or Subject To Liens	10,000	10,000
Electric generation and distribution facilities
Property, Plant and Equipment [Line Items]
Electric generation, distribution assets and other	$ 21,529	22,337
Electric generation and distribution facilities | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	8 years
Electric generation and distribution facilities | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	40 years
Other buildings
Property, Plant and Equipment [Line Items]
Electric generation, distribution assets and other	$ 1,971	1,906
Other buildings | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years
Other buildings | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	71 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Electric generation, distribution assets and other	$ 284	303
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	32 years
Other
Property, Plant and Equipment [Line Items]
Electric generation, distribution assets and other	$ 335	$ 365
Other | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years
Other | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	44 years