Revenue Recognition (Disaggregation of Revenue) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating revenue from contracts with customers		$ 0	$ 1	$ 1	$ 4
Total Operating Revenues	[1]	755	795	2,051	1,158
Electric Operations
Operating revenue from contracts with customers		688	721	1,773	861
Other revenues		3	7	12	8
Total Operating Revenues		691	728	1,785	869
Gas Distribution
Operating revenue from contracts with customers		64	67	266	289
Other revenues		0	0	0	0
Total Operating Revenues		64	67	266	289
Residential | Electric Operations
Operating revenue from contracts with customers		349	354	862	364
Residential | Gas Distribution
Operating revenue from contracts with customers		27	24	139	133
Commercial | Electric Operations
Operating revenue from contracts with customers		216	229	568	296
Commercial | Gas Distribution
Operating revenue from contracts with customers		18	19	71	80
Industrial | Electric Operations
Operating revenue from contracts with customers		90	101	253	119
Industrial | Gas Distribution
Operating revenue from contracts with customers		15	18	44	63
Other | Electric Operations
Operating revenue from contracts with customers		33	37	90	82
Other | Gas Distribution
Operating revenue from contracts with customers		$ 4	$ 6	$ 12	$ 13

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