Segment Information (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021		Mar. 31, 2020
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Electric		$ 733		$ 712
Net income		167		129
Regulated Operating Revenue, Gas		415		332
Unregulated Operating Revenue		13		13
Regulated and Unregulated Operating Revenue		1,161		1,057
Affiliate Revenue		1		1
Total revenues
Segment Reporting Information [Line Items]
Regulated and Unregulated Operating Revenue	[1]	1,161		1,057
Regulated Electric
Segment Reporting Information [Line Items]
Net income		81		74
Regulated Electric | Total revenues
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Electric		733		712
Regulated Natural Gas
Segment Reporting Information [Line Items]
Net income		83		52
Regulated Natural Gas | Total revenues
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Gas		415		332
All Other
Segment Reporting Information [Line Items]
Net income		3		3
All Other | Total revenues
Segment Reporting Information [Line Items]
Unregulated Operating Revenue		$ 13	[2]	$ 13	[1]

[1] Operating revenues include $1 million of other affiliate revenue for the three months ended March 31, 2021 and 2020.

[2] Operating revenues include $1 million of other affiliate revenue for the three months ended March 31, 2021 and 2020.