Segments and Related Information (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Operating revenue, Regulated Natural Gas										$ 1,355	$ 1,024	$ 1,161
Unregulated Operating Revenue										47	43	43
Regulated and Unregulated Operating Revenue		$ 1,134	$ 1,081	$ 911	$ 1,057	$ 1,134	$ 1,081	$ 911	$ 1,057	4,815	4,183	4,237
Depreciation and amortization										744	655	602
Interest charges and financing costs										234	224	224
Total income tax expense										33	45	80
Net income (loss)		$ 133	$ 218	$ 108	$ 129	$ 133	$ 218	$ 108	$ 129	660	588	578
Intercompany Revenue										5	5	5
Regulated Electric
Segment Reporting Information [Line Items]
Revenues Including Intersegment Revenues										3,414	3,117	3,034
Depreciation and amortization										566	497	455
Interest charges and financing costs										179	173	173
Total income tax expense										(16)	13	45
Net income (loss)										495	460	465
Regulated Natural Gas
Segment Reporting Information [Line Items]
Revenues Including Intersegment Revenues										1,355	1,024	1,161
Depreciation and amortization										171	152	141
Interest charges and financing costs										53	50	50
Total income tax expense										45	29	33
Net income (loss)										168	126	119
All Other
Segment Reporting Information [Line Items]
Depreciation and amortization										7	6	6
Interest charges and financing costs										2	1	1
Total income tax expense										4	3	2
Net income (loss)										(3)	2	(6)
Total revenues
Segment Reporting Information [Line Items]
Regulated and Unregulated Operating Revenue	[1]									4,816	4,184	4,238
Total revenues | Regulated Electric
Segment Reporting Information [Line Items]
Electric										3,413	3,116	3,033
Total revenues | All Other
Segment Reporting Information [Line Items]
Unregulated Operating Revenue	[1]									47	43	43
Intersegment Eliminations
Segment Reporting Information [Line Items]
Regulated and Unregulated Operating Revenue										(1)	(1)	(1)
Intersegment Eliminations | Regulated Electric
Segment Reporting Information [Line Items]
Electric										$ 1	$ 1	$ 1

[1] Operating revenues include $5 million of other affiliate revenue for the years ended Dec. 31, 2021, 2020 and 2019, respectively. See Note 13 for further information.