Segment Information (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Net income		$ 32	$ 34
Natural gas		57	45
Regulated and Unregulated Operating Revenue		281	257
Affiliate Revenue		46	41
Total revenues
Segment Reporting Information [Line Items]
Regulated and Unregulated Operating Revenue	[1]	281	257
Regulated Electric
Segment Reporting Information [Line Items]
Net income		24	25
Regulated Electric | Total revenues
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Electric	[1]	224	212
Regulated Natural Gas
Segment Reporting Information [Line Items]
Net income		8	9
Regulated Natural Gas | Total revenues
Segment Reporting Information [Line Items]
Natural gas		$ 57	$ 45

[1] Operating revenues include $46 million and $41 million of affiliate electric revenue for the three months ended March 31, 2021 and 2020, respectively.