Other Income Tax Matters - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020		Dec. 31, 2019
Income Tax [Line Items]
Federal NOL carryforward		$ 77	$ 77	$ 0
Federal tax credit carryforwards		704	704	543
State NOL carryforwards		344	344	151
Valuation allowances for state NOL carryforwards		(1)	(1)	(1)
State tax credit carryforwards, net of federal detriment (a)	[1]	78	78	71
Valuation allowances for state credit carryforwards, net of federal benefit (b)	[2]	$ (64)	$ (64)	$ (59)
Federal statutory rate			21.00%	21.00%		21.00%
State income tax on pretax income, net of federal tax effect			7.00%	7.00%		7.10%
Wind PTCs			(27.80%)	(19.30%)		(11.80%)
Plant regulatory differences (a)	[3]		(8.10%)	(7.20%)		(7.40%)
Other tax credits, net NOL & tax credit allowances			(1.40%)	(1.20%)		(1.50%)
Change in unrecognized tax benefits			0.50%	1.00%		0.50%
NOL Carryback		0.00%		(2.10%)		0.00%
Other, net			0.20%	(0.20%)		0.10%
Effective income tax rate			(8.60%)	(1.00%)		8.00%
Income tax (benefit) expense			$ (48)	$ (6)		$ 47
Deferred tax expense excluding items below			109	61		97
Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities			(145)	(127)		(135)
Tax expense allocated to other comprehensive income, adoption of ASC Topic 326, and other			0	(1)		(1)
Deferred tax benefit		$ (36)	(36)	(67)		39
Deferred fuel costs		92	92	7	[4]
Present value of minimum obligation		443	443
income tax expense [Member]
Income Tax [Line Items]
Current federal tax (benefit) expense			(10)	41		80
Current state tax (benefit) expense			(1)	12		8
Current change in unrecognized tax expense (benefit)			1	9		(1)
Deferred federal tax benefit			(87)	(102)		(86)
Deferred state tax expense			49	38		43
Deferred change in unrecognized tax expense (benefit)			2	(3)		4
Deferred ITCs			(2)	(1)		(1)
Income tax (benefit) expense			(48)	(6)		$ 47
Net Deferred Tax Liablility [Member]
Income Tax [Line Items]
Federal tax credit carryforwards		782	782	614	[4]
Deferred ITCs			5	5	[4]
Deferred tax benefit		(1,291)	(1,291)	(1,145)	[4]
Differences between book and tax bases of property			2,679	2,482	[4]
Regulatory assets		260	260	270	[4]
Operating lease assets		123	123	147	[4]
Pension expense		73	73	72	[4]
Other		13	13	7	[4]
Total deferred tax liabilities		3,240	3,240	2,985	[4]
Regulatory Liabilities		325	325	349	[4]
Present value of minimum obligation		123	123	147	[4]
NOL and tax credit valuation allowances		(64)	(64)	(59)	[4]
Other employee benefits		32	32	38	[4]
NOL carryforward		43	43	12	[4]
Other		45	45	39	[4]
Net deferred tax liability		1,949	1,949	1,840	[4]
State and Local Jurisdiction
Income Tax [Line Items]
Federal detriment		21	21	19
Federal Benefit		$ 17	$ 17	$ 16

[1] State tax credit carryforwards are net of federal detriment of $21 million and $19 million as of Dec. 31, 2021 and 2020, respectively.

[2] Valuation allowances for state tax credit carryforwards were net of federal benefit of $17 million and $16 million as of Dec. 31, 2021 and 2020, respectively.

[3] 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.

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