Revenue Recognition (Disaggregation of Revenue) (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating revenue from contracts with customers		$ 0	$ 0	$ 0	$ 1
Total Operating Revenues	[1]	692	624	1,436	1,296
Electric Operations
Operating revenue from contracts with customers		603	548	1,174	1,085
Other revenues		0	7	8	9
Total Operating Revenues		603	555	1,182	1,094
Gas Distribution
Operating revenue from contracts with customers		89	69	253	202
Other revenues		0	0	1	0
Total Operating Revenues		89	69	254	202
Residential | Electric Operations
Operating revenue from contracts with customers		271	261	546	513
Residential | Gas Distribution
Operating revenue from contracts with customers		38	33	136	112
Commercial | Electric Operations
Operating revenue from contracts with customers		199	177	374	352
Commercial | Gas Distribution
Operating revenue from contracts with customers		26	20	65	53
Industrial | Electric Operations
Operating revenue from contracts with customers		95	83	183	163
Industrial | Gas Distribution
Operating revenue from contracts with customers		18	12	40	29
Other | Electric Operations
Operating revenue from contracts with customers		38	27	71	57
Other | Gas Distribution
Operating revenue from contracts with customers		$ 7	$ 4	$ 12	$ 8

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