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]
Net income	$ 36		$ 40		$ 82		$ 85
Regulated and Unregulated Operating Revenue	274		251		810		726
Affiliate Revenue	49		41		141		123
Natural gas	22		15		110		79
Total revenues
Segment Reporting Information [Line Items]
Regulated and Unregulated Operating Revenue	275	[1]	251	[1]	811	[2]	726	[2]
Intersegment Eliminations
Segment Reporting Information [Line Items]
Regulated and Unregulated Operating Revenue	(1)		0		(1)		0
Regulated Electric
Segment Reporting Information [Line Items]
Net income	38		40		77		81
Regulated Electric | Total revenues
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Electric	252	[1]	236	[1]	700	[2]	647	[2]
Regulated Natural Gas
Segment Reporting Information [Line Items]
Net income	(4)		(2)		3		3
Revenues Including Intersegment Revenues	23		15		111		79
Regulated Natural Gas | Total revenues
Segment Reporting Information [Line Items]
Natural gas	22		15		110		79
Regulated Natural Gas | Intersegment Eliminations
Segment Reporting Information [Line Items]
Natural gas	1		0		1		0
All Other
Segment Reporting Information [Line Items]
Net income	$ 2		$ 2		$ 2		$ 1

[1] Total revenues include $49 million and $41 million of affiliate electric revenue for the three months ended Sept. 30, 2021 and 2020, respectively.

[2] Total revenues include $141 million and $123 million of affiliate electric revenue for the nine months ended Sept. 30, 2021 and 2020, respectively.