Segment Information (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2021		Sep. 30, 2020		Sep. 30, 2021		Sep. 30, 2020
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Electric	$ 1,048		$ 916		$ 2,608		$ 2,343
Net income	215		218		516		455
Unregulated Operating Revenue	12		9		34		32
Regulated and Unregulated Operating Revenue	1,237		1,081		3,572	[1]	3,049	[1]
Affiliate Revenue	1		1		3		3
Total revenues
Segment Reporting Information [Line Items]
Regulated and Unregulated Operating Revenue	1,237	[1]	1,081	[1]	3,573	[2]	3,049	[2]
Intersegment Eliminations
Segment Reporting Information [Line Items]
Regulated and Unregulated Operating Revenue					(1)		0
Regulated Electric
Segment Reporting Information [Line Items]
Revenues Including Intersegment Revenues	1,048		916		2,609		2,343
Net income	212		215		400		378
Regulated Electric | Total revenues
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Electric					2,608		2,343
Regulated Electric | Intersegment Eliminations
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Electric					1		0
Regulated Natural Gas
Segment Reporting Information [Line Items]
Revenues Including Intersegment Revenues	177		156		930		674
Net income	8		4		121		72
All Other
Segment Reporting Information [Line Items]
Net income	(5)		(1)		(5)		5
All Other | Total revenues
Segment Reporting Information [Line Items]
Unregulated Operating Revenue	$ 12	[3]	$ 9	[1]	$ 34	[2]	$ 32	[2]

[1] Total revenues include $1 million of other affiliate revenue for both the three months ended Sept. 30, 2021 and 2020.

[2] Total revenues include $3 million of other affiliate revenue for both the nine months ended Sept. 30, 2021 and 2020.

[3] Total revenues include $1 million of other affiliate revenue for both the three months ended Sept. 30, 2021 and 2020.