Income Taxes (Tables)

6 Months Ended

Jun. 30, 2019

Income Tax Disclosure [Abstract]

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

The following table reconciles the difference between the statutory rate and the ETR:

	Six Months Ended June 30,
	2019		2018
Federal statutory rate	21.0	%	21.0	%
State tax (net of federal tax effect)	2.1		2.4
Increases (decreases) in tax from:
Plant regulatory differences (a)	(4.8	)	(4.4	)
Prior period adjustments	(0.7	)	(0.2	)
Other tax credits (net)	(0.6	)	(0.8	)
Wind PTCs	(0.2	)	—
Other (net)	(0.4	)	0.4
Effective income tax rate	16.4	%	18.4	%

^(a)

Regulatory differences for income tax primarily relate to the flow back of excess deferred taxes to customers through the average rate assumption method and the impact of AFUDC - Equity. Year-to-date variations primarily relates to the deferral of the flow back of excess deferred taxes in 2018, as a result of pending regulatory decisions. Treatment of most tax reform items was established prior to the first quarter of 2019, resulting in a reduction in deferred amounts. Income tax benefits associated with the flow back 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 federal income tax returns expire as follows:

Tax Year(s)	Expiration
2009 - 2013	June 2020
2014 - 2016	September 2020
2017	September 2021

Reconciliation of Unrecognized Tax Benefits

Unrecognized tax benefits - permanent vs temporary:

(Millions of Dollars)	June 30, 2019		Dec. 31, 2018
Unrecognized tax benefit — Permanent tax positions	$	3.3	$	3.0
Unrecognized tax benefit — Temporary tax positions	1.5		1.5
Total unrecognized tax benefit	$	4.8	$	4.5

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, 2019			Dec. 31, 2018
NOL and tax credit carryforwards	$	(4.1	)	$	(3.8	)