Property, Plant and Equipment (Regulated and Non-Regulated Generation and Distribution PP&E) (Details) - USD ($) $ in Millions	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)
Net electric generation and distribution assets and other	16,177	16,992
Regulated Operation [Member]
Property, Plant and Equipment [Line Items]
Electric generation, distribution assets and other	8,093	7,815
Accumulated depreciation	(3,357)	(3,299)
Net electric generation and distribution assets and other	4,736	4,516
Unregulated Operation [Member]
Property, Plant and Equipment [Line Items]
Electric generation, distribution assets and other	16,026	17,096
Accumulated depreciation	(4,585)	(4,620)
Net electric generation and distribution assets and other	$ 11,441	$ 12,476