Other Income Tax Matters (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020		Dec. 31, 2019
Income Tax [Line Items]
Federal NOL carryforward		$ 336	$ 0
Federal tax credit carryforwards		187	83
State NOL carryforwards		$ 111	$ 1
Federal statutory rate		21.00%	21.00%	[1]	21.00%	[1]
State income tax on pretax income, net of federal tax effect		2.50%	2.30%	[1]	2.20%	[1]
Wind PTCs		(39.70%)	(18.30%)	[1]	(7.90%)	[1]
Plant regulatory differences (b)	[2]	(4.80%)	(6.40%)	[1]	(5.00%)	[1]
Amortization of excess nonplant deferred taxes		(1.10%)	(0.80%)	[1]	(0.90%)	[1]
Change in unrecognized tax benefits		0.50%	0.30%	[1]	0.20%	[1]
Other, net		(1.20%)	(1.60%)	[1]	(0.60%)	[1]
Effective income tax rate		(22.80%)	(3.50%)	[1]	9.00%	[1]
Total income tax (benefit) expense		$ (59)	$ (10)		$ 26
Deferred tax (benefit) expense excluding items below		(23)	53		53
Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities		(24)	(31)		(24)
Total deferred tax assets		(47)	22		29
Deferred fuel costs		34	(9)	[3]
Operating lease liabilities		464
NOL carryforward		76	0	[3]
income tax expense [Member]
Income Tax [Line Items]
Current federal tax benefit		(11)	(31)		(4)
Current state tax (benefit) expense		(1)	(1)		1
Current change in unrecognized tax expense		0	0		0
Deferred federal tax (benefit) expense		(57)	13		22
Deferred state tax expense		9	8		6
Deferred change in unrecognized tax expense		1	1		1
Total income tax (benefit) expense		(59)	(10)		$ 26
Net Deferred Tax Liablility [Member]
Income Tax [Line Items]
Federal tax credit carryforwards		187	83	[3]
Total deferred tax assets		478	307	[3]
Differences between book and tax bases of property		942	838	[3]
Operating lease assets		103	109	[3]
Regulatory assets		65	59	[3]
Pension expense		34	33	[3]
Other		2	2	[3]
Total deferred tax liabilities		1,180	1,032	[3]
Operating lease liabilities		103	109	[3]
Regulatory liabilities		98	104	[3]
Other employee benefits		7	7	[3]
Other		7	4	[3]
Net deferred tax liability		$ 702	$ 725	[3]

[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.