Fair Value of Financial Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Gross Notional Amounts of Commodity FTRs

The following table details the gross notional amounts of commodity FTRs at Dec. 31, 2017 and 2016:

(Amounts in Thousands)(a)	Dec. 31, 2017	Dec. 31, 2016
MWh of electricity	4,251	2,685

^(a) Amounts are not reflective of net positions in the underlying commodities.

Financial Impact of Qualifying Cash Flow Hedges on Accumulated Other Comprehensive Loss

Financial Impact of Qualifying Cash Flow Hedges — The impact of qualifying interest rate cash flow hedges on SPS’ accumulated other comprehensive loss, included in the statements of common stockholder’s equity and in the statements of comprehensive income, is detailed in the following table:

(Thousands of Dollars)	2017			2016			2015
Accumulated other comprehensive loss related to cash flow hedges at Jan. 1	$	(678	)	$	(817	)	$	(989	)
After-tax net realized losses on derivative transactions reclassified into earnings	39			139			172
Accumulated other comprehensive loss related to cash flow hedges at Dec. 31	$	(639	)	$	(678	)	$	(817	)

Derivative Assets and Liabilities Measured at Fair Value on a Recurring Basis by Hierarchy Level

Recurring Fair Value Measurements — The following table presents for each of the fair value hierarchy levels, SPS’ derivative assets and liabilities measured at fair value on a recurring basis at Dec. 31, 2017:

	Dec. 31, 2017
	Fair Value						Fair Value Total		Counterparty Netting (b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative assets
Other derivative instruments:
Electric commodity	$	—	$	—	$	14,717	$	14,717	$	(1,994	)	$	12,723
Total current derivative assets	$	—	$	—	$	14,717	$	14,717	$	(1,994	)	12,723
PPAs (a)												3,159
Current derivative instruments												$	15,882
Noncurrent derivative assets
PPAs (a)												$	18,954
Noncurrent derivative instruments												$	18,954
Current derivative liabilities
Other derivative instruments:
Electric commodity	$	—	$	—	$	1,994	$	1,994	$	(1,994	)	$	—
Total current derivative liabilities	$	—	$	—	$	1,994	$	1,994	$	(1,994	)	—
PPAs (a)												3,565
Current derivative instruments												$	3,565
Noncurrent derivative liabilities
PPAs (a)												$	19,949
Noncurrent derivative instruments												$	19,949

^(a)  During 2006, SPS qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

^(b)  SPS nets derivative instruments and related collateral in its balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at Dec. 31, 2017. At Dec. 31, 2017, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

The following table presents for each of the fair value hierarchy levels, SPS’ derivative assets and liabilities measured at fair value on a recurring basis at Dec. 31, 2016:

	Dec. 31, 2016
	Fair Value						Fair Value Total		Counterparty Netting (b)
(Thousands of Dollars)	Level 1		Level 2		Level 3							Total
Current derivative assets
Other derivative instruments:
Electric commodity	$	—	$	—	$	3,254	$	3,254	$	(1,299	)	$	1,955
Total current derivative assets	$	—	$	—	$	3,254	$	3,254	$	(1,299	)	1,955
PPAs (a)												3,159
Current derivative instruments												$	5,114
Noncurrent derivative assets
PPAs (a)												$	22,113
Noncurrent derivative instruments												$	22,113
Current derivative liabilities
Other derivative instruments:
Electric commodity	$	—	$	—	$	1,299	$	1,299	$	(1,299	)	$	—
Total current derivative liabilities	$	—	$	—	$	1,299	$	1,299	$	(1,299	)	—
PPAs (a)												3,565
Current derivative instruments												$	3,565
Noncurrent derivative liabilities
PPAs (a)												$	23,513
Noncurrent derivative instruments												$	23,513

^(a) During 2006, SPS qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.

^(b) SPS nets derivative instruments and related collateral in its balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at Dec. 31, 2016. At Dec. 31, 2016, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

Changes in Level 3 Commodity Derivatives

The following table presents the changes in Level 3 commodity derivatives for the years ended Dec. 31, 2017, 2016 and 2015:

	Year Ended Dec. 31
(Thousands of Dollars)	2017			2016			2015
Balance at Jan. 1	$	1,955		$	5,060		$	15,884
Purchases	41,176			7,616			23,425
Settlements	(55,758		)	(41,923		)	(31,703		)
Net transactions recorded during the period:
Net gains (losses) recognized as regulatory assets	25,350			31,202			(2,546		)
Balance at Dec. 31	$	12,723		$	1,955		$	5,060

Carrying Amount and Fair Value of Long-term Debt

As of Dec. 31, 2017 and 2016, other financial instruments for which the carrying amount did not equal fair value were as follows:

	2017				2016
(Thousands of Dollars)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term debt, including current portion	$	1,829,941	$	2,001,992	$	1,635,858	$	1,741,502