Income Taxes (Tables)

6 Months Ended

Jun. 30, 2021

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

Difference between the statutory rate and ETR:

	Six Months Ended June 30
	2021		2020 (a)
Federal statutory rate	21.0	%	21.0	%
State tax (net of federal tax effect)	2.6		2.3
Decreases in tax from:
Wind PTCs	(61.6)		(26.7)
Plant regulatory differences (b)	(5.0)		(6.4)
Amortization of excess nonplant deferred taxes	(1.2)		(0.9)
Other (net)	(0.6)		(2.2)
Effective income tax rate	(44.8)	%	(12.9)	%

(a)Prior periods have been restated to conform to current year presentation.

(b)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.

Summary of Statute of Limitations Applicable to Open Tax Years [Table Text Block]

Federal Audits — SPS is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. Statute of limitations applicable to Xcel Energy’s consolidated federal income tax returns expire as follows:

Tax Years	Expiration
2014 — 2016	January 2022
2017	September 2021

Reconciliation of Unrecognized Tax Benefits

Unrecognized tax benefits — permanent vs temporary:

(Millions of Dollars)	June 30, 2021		Dec. 31, 2020
Unrecognized tax benefit — Permanent tax positions	$	3	$	3
Unrecognized tax benefit — Temporary tax positions	4		4
Total unrecognized tax benefit	$	7	$	7

Tax Benefits Associated with NOL and Tax Credit Carryforwards

Unrecognized tax benefits were reduced by tax benefits associated with NOL and tax credit carryforwards:

(Millions of Dollars)	June 30, 2021		Dec. 31, 2020
NOL and tax credit carryforwards	$	(7)	$	(6)

Interest Payable related to Unrecognized Tax Benefits

Interest payable related to unrecognized tax benefits:

(Millions of Dollars)	June 30, 2021		Dec. 31, 2020
(Payable) receivable for interest related to unrecognized tax benefits at beginning of period	$	(1)	$	1
Interest expense related to unrecognized tax benefits	—		(2)
Payable for interest related to unrecognized tax benefits at end of period	$	(1)	$	(1)