Other Income Tax Matters - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020		Dec. 31, 2019
Income Tax Examination [Line Items]
Federal detriment		$ 5	$ 5
Federal Benefit		2	2
Federal NOL carryforward		161	0
Federal tax credit carryforwards		259	143
State NOL carryforwards		342	190
state tax credit carryforward, net of federal detirment	[1]	17	18
valuation allowances for state credit carryforwards, net of federal benefit	[2]	$ (8)	$ (8)
Federal statutory rate		21.00%	21.00%	[3]	21.00%	[3]
State income tax on pretax income, net of federal tax effect		3.60%	3.60%	[3]	3.60%	[3]
Wind PTCs		(14.30%)	(10.30%)	[3]	(7.50%)	[3]
Plant regulatory differences (b)	[4]	(4.60%)	(5.00%)	[3]	(3.30%)	[3]
Other tax credits, net NOL & tax credit allowances		(1.00%)	(1.10%)	[3]	(1.30%)	[3]
Change in unrecognized tax benefits		0.30%	(0.20%)	[3]	0.30%	[3]
Other, net		(0.20%)	(0.90%)	[3]	(0.60%)	[3]
Effective income tax rate		4.80%	7.10%	[3]	12.20%	[3]
Total income tax expense		$ 33	$ 45		$ 80
Deferred tax expense excluding items below		63	46		132
Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities		(42)	(43)		(35)
Tax expense allocated to other comprehensive income, adoption of ASC Topic 326, and other		0	(1)		0
Total deferred tax assets		21	2		97
Deferred fuel costs		126	(3)	[3]
Operating lease liabilities		435
Bad debts		10	8	[5]
Tax credit valuation allowances		(8)	(8)	[5]
income tax expense [Member]
Income Tax Examination [Line Items]
Current federal tax expense (benefit)		16	44		(9)
Current state tax expense (benefit)		0	4		(5)
Current change in unrecognized tax benefit		(1)	(3)		(1)
Deferred federal tax (benefit) expense		(13)	(26)		61
Deferred state tax expense		31	26		33
Deferred change in unrecognized tax expense		3	2		3
Deferred ITCs		3	2		(2)
Total income tax expense		33	45		$ 80
Net Deferred Tax Liablility [Member]
Income Tax Examination [Line Items]
Deferred ITCs		(8)	(5)	[5]
Total deferred tax assets		786	643	[5]
Differences between book and tax bases of property		2,226	2,132	[5]
Regulatory assets		258	257	[5]
Operating lease assets		106	129	[5]
Pension expense and other employee benefits		23	19	[5]
Other		7	6	[5]
Total deferred tax liabilities		2,746	2,540	[5]
Regulatory liabilities		323	319	[5]
Tax credit carryforward		276	161	[5]
Operating lease liabilities		106	129	[5]
NOL carryforward		46	7	[5]
Other		25	22	[5]
Net deferred tax liability		$ 1,960	$ 1,897	[5]

[1] State tax credit carryforwards are net of federal detriment of $5 million as of Dec. 31, 2021 and 2020.

[2] Valuation allowances for state tax credit carryforwards were net of federal benefit of $2 million as of Dec. 31, 2021 and 2020.

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

[4] 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 and additional prepaid pension asset amortization.

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