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]
Unregulated Operating Revenue										$ 1	$ 0	$ 0
Regulated and Unregulated Operating Revenue		$ 248	$ 251	$ 218	$ 257	$ 248	$ 251	$ 218	$ 257	1,105	974	981
Depreciation and amortization										147	156	138
Interest charges and financing costs										40	38	38
Total income tax expense (benefit)										30	(7)	16
Net income		$ 21	$ 40	$ 12	$ 34	$ 21	$ 40	$ 12	$ 34	108	107	79
Electric, affiliates										189	168	177
Natural gas										182	119	136
Regulated Electric
Segment Reporting Information [Line Items]
Revenues Including Intersegment Revenues										922	856	845
Depreciation and amortization										120	108	109
Interest charges and financing costs										36	34	34
Total income tax expense (benefit)										27	12	13
Net income										98	98	68
Regulated Natural Gas
Segment Reporting Information [Line Items]
Revenues Including Intersegment Revenues										183	119	136
Depreciation and amortization										27	48	29
Interest charges and financing costs										4	4	4
Total income tax expense (benefit)										2	(20)	2
Net income										7	7	10
All Other
Segment Reporting Information [Line Items]
Total income tax expense (benefit)										1	1	1
Net income										3	2	1
Total revenues
Segment Reporting Information [Line Items]
Regulated and Unregulated Operating Revenue	[1]									1,106	975	981
Total revenues | Regulated Electric
Segment Reporting Information [Line Items]
Operating revenue, Regulated Electric	[1]									922	855	845
Total revenues | Regulated Natural Gas
Segment Reporting Information [Line Items]
Natural gas										182	119	136
Total revenues | All Other
Segment Reporting Information [Line Items]
Unregulated Operating Revenue										1	0	0
Intersegment Eliminations
Segment Reporting Information [Line Items]
Regulated and Unregulated Operating Revenue										(1)	(1)	0
Intersegment Eliminations | Regulated Electric
Segment Reporting Information [Line Items]
Operating revenue, Regulated Electric										0	1	0
Intersegment Eliminations | Regulated Natural Gas
Segment Reporting Information [Line Items]
Natural gas										$ 1	$ 0	$ 0

[1] (a)    Operating revenues include $189 million, $168 million and $177 million of affiliate electric revenue for the years ended Dec. 31, 2021, 2020 and 2019, respectively. See Note 12 for further information.