Other Comprehensive Income (Tables)

12 Months Ended

Dec. 31, 2017

Stockholders' Equity Note [Abstract]

Changes in Accumulated Other Comprehensive Income (Loss), Net of Tax

Changes in accumulated other comprehensive loss, net of tax, for the years ended Dec. 31, 2017 and 2016 were as follows:

	Year Ended Dec. 31, 2017
(Thousands of Dollars)	Gains and Losses on Cash Flow Hedges			Defined Benefit Pension and Postretirement Items			Total
Accumulated other comprehensive loss at Jan. 1	$	(678	)	$	(612	)	$	(1,290	)
Losses reclassified from net accumulated other comprehensive loss	39			44			83
Net current period other comprehensive income	39			44			83
Adoption of ASU No. 2018-02 (a)	(137		)	(123		)	(260		)
Accumulated other comprehensive loss at Dec. 31	$	(776	)	$	(691	)	$	(1,467	)

^(a)  In 2017, SPS implemented ASU No. 2018-02 related to the TCJA, which resulted in reclassification of certain credit balances within accumulated other comprehensive loss to retained earnings. For further information, see Note 2.

	Year Ended Dec. 31, 2016
(Thousands of Dollars)	Gains and Losses on Cash Flow Hedges			Defined Benefit Pension and Postretirement Items			Total
Accumulated other comprehensive loss at Jan. 1	$	(817	)	$	(464	)	$	(1,281	)
Other comprehensive loss before reclassifications	—			(148		)	(148		)
Losses reclassified from net accumulated other comprehensive loss	139			—			139
Net current period other comprehensive income (loss)	139			(148		)	(9		)
Accumulated other comprehensive loss at Dec. 31	$	(678	)	$	(612	)	$	(1,290	)

Reclassifications out of Accumulated Other Comprehensive Loss

Reclassifications from accumulated other comprehensive loss for the years ended Dec. 31, 2017 and 2016 were as follows:

	Amounts Reclassified from Accumulated Other Comprehensive Loss
(Thousands of Dollars)	Year Ended Dec. 31, 2017				Year Ended Dec. 31, 2016
Losses on cash flow hedges:
Interest rate derivatives	$	63		(a)	$	219		(a)
Total, pre-tax	63				219
Tax benefit	(24		)		(80		)
Total, net of tax	39				139
Defined benefit pension and postretirement losses:
Amortization of net loss	69			(b)	—			(b)
Total, pre-tax	69				—
Tax benefit	(25		)		—
Total, net of tax	44				—
Total amounts reclassified, net of tax	$	83			$	139

^(a)  Included in interest charges.

^(b)  Included in the computation of net periodic pension and postretirement benefit costs. See Note 7 for details regarding these benefit plans.