Other Income Tax Matters (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020		Dec. 31, 2019
Income Tax Examination [Line Items]
Tax credit carryforward		$ 8	$ 7
State NOL carryforward		$ 2	$ 2
Federal statutory rate		21.00%	21.00%		21.00%	[1]
State income tax on pretax income, net of federal tax effect		6.20%	6.20%		6.20%	[1]
Plant regulatory differences (b)	[2]	(4.10%)	(19.30%)		(5.20%)	[1]
Other tax credits, net NOL & tax credit allowances		(1.00%)	(1.50%)		(1.80%)	[1]
Change in unrecognized tax benefits		0.30%	(0.80%)		0.70%	[1]
Amortization of excess nonplant deferred taxes		0.00%	(12.60%)		0.00%	[1]
Reversal of prior regulatory differences		0.00%	0.00%		(3.60%)	[1]
Other, net		(0.70%)	0.00%		(0.50%)	[1]
Effective income tax rate		21.70%	(7.00%)		16.80%	[1]
Total income tax expense (benefit)		$ 30	$ (7)		$ 16
Deferred tax expense excluding items below		18	9		17
Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities		(10)	(45)		(12)
Other		1	0		0
Deferred tax expense (benefit)		9	36		(5)
Deferred fuel costs		8	0	[3]
Environmental remediation		5	6	[1]
income tax expense [Member]
Income Tax Examination [Line Items]
Current federal tax expense		17	25		6
Current state tax expense		4	6		5
Current change in unrecognized tax (benefit) expense		0	(1)		1
Deferred federal tax expense (benefit)		3	(37)		3
Deferred state tax expense		6	1		2
Deferred ITCs		0	(1)		(1)
Total income tax expense (benefit)		30	(7)		$ 16
Net Deferred Tax Liablility [Member]
Income Tax Examination [Line Items]
Tax credit carryforward		8	8	[1]
Deferred ITCs		(2)	(3)	[1]
Other		4	4	[1]
Deferred tax expense (benefit)		(61)	(70)	[1]
Difference between book and tax bases of property		331	324	[1]
Regulatory assets		29	32	[1]
Pension expense		11	12	[1]
Other		7	9	[1]
Total deferred tax liabilities		386	377	[1]
Regulatory liabilities		38	41	[1]
Other employee benefits		4	4	[1]
Rate refund		0	4	[1]
Net deferred tax liability		$ 325	$ 307	[1]

[1] Prior periods have been reclassified to conform to current year presentation.

[2] Regulatory differences for income tax primarily relate to the credit of excess deferred taxes to customers through the average rate assumption method. Income tax benefits associated with the credit of excess deferred credits are offset by corresponding revenue reductions.

[3] Prior periods have been reclassified to conform to current year presentation.