Revenue - Schedule of Revenues Disaggregated by Major Source for Reportable Segments (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Operating revenues	$ 1,652	$ 1,767
Lease Income	1	1
Derivative revenue	70	41
Alternative revenue programs	56	16
Other revenue	10	17
Revenues	1,789	1,842
Electricity
Segment Reporting Information [Line Items]
Operating revenues	873	913
Natural Gas
Segment Reporting Information [Line Items]
Operating revenues	507	625
Wind Energy
Segment Reporting Information [Line Items]
Operating revenues	211	182
Solar Energy
Segment Reporting Information [Line Items]
Operating revenues	4	5
Thermal Energy
Segment Reporting Information [Line Items]
Operating revenues	10	16
Other
Segment Reporting Information [Line Items]
Operating revenues	47	26
Networks
Segment Reporting Information [Line Items]
Operating revenues	1,399	1,575
Lease Income	1	1
Alternative revenue programs	56	16
Other revenue	5	12
Revenues	1,461	1,604
Networks | Electricity
Segment Reporting Information [Line Items]
Operating revenues	873	913
Networks | Natural Gas
Segment Reporting Information [Line Items]
Operating revenues	507	625
Networks | Other
Segment Reporting Information [Line Items]
Operating revenues	19	37
Renewables
Segment Reporting Information [Line Items]
Operating revenues	253	196
Lease Income	0	0
Derivative revenue	70	41
Other revenue	5	5
Revenues	328	242
Renewables | Wind Energy
Segment Reporting Information [Line Items]
Operating revenues	211	182
Renewables | Solar Energy
Segment Reporting Information [Line Items]
Operating revenues	4	5
Renewables | Thermal Energy
Segment Reporting Information [Line Items]
Operating revenues	10	16
Renewables | Other
Segment Reporting Information [Line Items]
Operating revenues	28	(7)
Other
Segment Reporting Information [Line Items]
Operating revenues	0	(4)
Lease Income	0	0
Revenues	0	(4)
Other | Other
Segment Reporting Information [Line Items]
Operating revenues	$ 0	$ (4)