Revenue Recognition (Disaggregation of Revenue) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Operating revenue from contracts with customers		$ 1	$ 1
Total Operating Revenues	[1]	672	(335)
Electric Operations
Operating revenue from contracts with customers		537	(482)
Other revenues		2	2
Total Operating Revenues		539	(480)
Gas Distribution
Operating revenue from contracts with customers		133	145
Other revenues		0	0
Total Operating Revenues		133	145
Residential | Electric Operations
Operating revenue from contracts with customers		252	(271)
Residential | Gas Distribution
Operating revenue from contracts with customers		79	78
Commercial | Electric Operations
Operating revenue from contracts with customers		175	(139)
Commercial | Gas Distribution
Operating revenue from contracts with customers		33	38
Industrial | Electric Operations
Operating revenue from contracts with customers		80	(82)
Industrial | Gas Distribution
Operating revenue from contracts with customers		17	26
Other | Electric Operations
Operating revenue from contracts with customers		30	10
Other | Gas Distribution
Operating revenue from contracts with customers		$ 4	$ 3

[1] See Note 12 for amounts attributable to affiliates.