Revenue Recognition (Disaggregation of Revenue) (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating revenue from contracts with customers		$ 0	$ 2	$ 1	$ 3
Total Operating Revenues	[1]	624	698	1,296	363
Electric Operations
Operating revenue from contracts with customers		548	622	1,085	140
Other revenues		7	(1)	9	1
Total Operating Revenues		555	621	1,094	141
Gas Distribution
Operating revenue from contracts with customers		69	77	202	222
Other revenues		0	0	0	0
Total Operating Revenues		69	77	202	222
Residential | Electric Operations
Operating revenue from contracts with customers		261	281	513	10
Residential | Gas Distribution
Operating revenue from contracts with customers		33	31	112	109
Commercial | Electric Operations
Operating revenue from contracts with customers		177	206	352	67
Commercial | Gas Distribution
Operating revenue from contracts with customers		20	23	53	61
Industrial | Electric Operations
Operating revenue from contracts with customers		83	100	163	18
Industrial | Gas Distribution
Operating revenue from contracts with customers		12	19	29	45
Other | Electric Operations
Operating revenue from contracts with customers		27	35	57	45
Other | Gas Distribution
Operating revenue from contracts with customers		$ 4	$ 4	$ 8	$ 7

[1] See Note 14 for amounts attributable to affiliates.