Property, Plant and Equipment, Net (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property, plant and equipment in service, net	$ 58,395	$ 58,142
Construction work-in-progress	2,757	2,627
Property, plant and equipment, net	61,152	60,769
Regulated assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	76,678	76,003
Accumulated depreciation and amortization	(23,084)	(22,682)
Property, plant and equipment in service, net	53,594	53,321
Construction work-in-progress	2,300	2,300
Regulated assets [Member] | Utility generation, transmission and distribution systems
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 69,880	69,248
Regulated assets [Member] | Utility generation, transmission and distribution systems | Minimum [Member]
Property, Plant and Equipment [Line Items]
Depreciable Life	5 years
Regulated assets [Member] | Utility generation, transmission and distribution systems | Maximum [Member]
Property, Plant and Equipment [Line Items]
Depreciable Life	80 years
Regulated assets [Member] | Interstate natural gas pipeline assets
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 6,798	6,755
Regulated assets [Member] | Interstate natural gas pipeline assets | Minimum [Member]
Property, Plant and Equipment [Line Items]
Depreciable Life	3 years
Regulated assets [Member] | Interstate natural gas pipeline assets | Maximum [Member]
Property, Plant and Equipment [Line Items]
Depreciable Life	80 years
Unregulated operation [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 5,665	5,626
Accumulated depreciation and amortization	(864)	(805)
Property, plant and equipment in service, net	4,801	4,821
Unregulated operation [Member] | Independent power plants
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 4,781	4,751
Unregulated operation [Member] | Independent power plants | Minimum [Member]
Property, Plant and Equipment [Line Items]
Depreciable Life	5 years
Unregulated operation [Member] | Independent power plants | Maximum [Member]
Property, Plant and Equipment [Line Items]
Depreciable Life	30 years
Unregulated operation [Member] | Other assets
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 884	$ 875
Unregulated operation [Member] | Other assets | Minimum [Member]
Property, Plant and Equipment [Line Items]
Depreciable Life	3 years
Unregulated operation [Member] | Other assets | Maximum [Member]
Property, Plant and Equipment [Line Items]
Depreciable Life	30 years