Segment Information (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Net income		$ 128	$ 107
Natural gas		204	206
Other		9	9
Regulated and Unregulated Operating Revenue		1,352	1,250
Affiliate Revenue		115	110
Total revenues
Segment Reporting Information [Line Items]
Regulated and Unregulated Operating Revenue	[1],[2]	1,352	1,250
Regulated Electric
Segment Reporting Information [Line Items]
Net income		107	86
Regulated Electric | Total revenues
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Electric	[1]	1,139	1,035
Regulated Natural Gas
Segment Reporting Information [Line Items]
Net income		20	23
Regulated Natural Gas | Total revenues
Segment Reporting Information [Line Items]
Natural gas	[2]	204	206
All Other
Segment Reporting Information [Line Items]
Net income		1	(2)
All Other | Total revenues
Segment Reporting Information [Line Items]
Other		$ 9	$ 9

[1] Total revenues include $115 million and $110 million of affiliate electric revenue for the three months ended March 31, 2021 and 2020.

[2] Total revenues include an immaterial amount of affiliate gas revenue for the three months ended March 31, 2021 and 2020.