Property, Plant and Equipment, Net (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property, plant and equipment in service, net	$ 58,933	$ 58,142
Construction work-in-progress	3,175	2,627
Property, plant and equipment, net	62,108	60,769
Regulated assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	77,182	76,003
Accumulated depreciation and amortization	(23,305)	(22,682)
Property, plant and equipment in service, net	53,877	53,321
Construction work-in-progress	2,600	2,300
Regulated assets [Member] | Utility generation, transmission and distribution systems
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 70,316	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	$ 6,866	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	$ 6,056	5,626
Accumulated depreciation and amortization	(1,000)	(805)
Property, plant and equipment in service, net	5,056	4,821
Unregulated operation [Member] | Independent power plants
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 5,073	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	$ 983	$ 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