Fair Value of Financial Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Gross Notional Amounts of Commodity FTRs

(Amounts in Millions) (a)	Dec. 31, 2020	Dec. 31, 2019
MWh of electricity	5	6

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

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

SPS’ derivative assets and liabilities measured at fair value on a recurring basis were as follows:

	Dec. 31, 2020												Dec. 31, 2019
	Fair Value						Fair Value Total		Netting (a)		Total		Fair Value						Fair Value Total		Netting (a)		Total
(Millions of Dollars)	Level 1		Level 2		Level 3								Level 1		Level 2		Level 3
Current derivative assets
Other derivative instruments:
Electric commodity	$	—	$	—	$	7	$	7	$	—	$	7	$	—	$	—	$	12	$	12	$	—	$	12
Total current derivative assets	$	—	$	—	$	7	$	7	$	—	7		$	—	$	—	$	12	$	12	$	—	12
PPAs (b)											3												3
Current derivative instruments											$	10											$	15
Noncurrent derivative assets
PPAs (b)											$	9											$	13
Noncurrent derivative instruments											$	9											$	13
Current derivative liabilities
Other derivative instruments:
PPAs (b)											$	4											$	4
Current derivative instruments											$	4											$	4
Noncurrent derivative liabilities
PPAs (b)											$	9											$	13
Noncurrent derivative instruments											$	9											$	13

(a)SPS nets derivative instruments and related collateral on its balance sheets 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, 2020 and 2019. At Dec. 31, 2020 and 2019, derivative assets and liabilities include no obligations to return cash collateral, respectively. At Dec. 31, 2020 and 2019, derivative assets and liabilities include no rights to reclaim cash collateral, respectively. The counterparty netting excludes settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

(b)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.

Changes in Level 3 Commodity Derivatives

Changes in Level 3 commodity derivatives for the years ended Dec. 31, 2020, 2019 and 2018:

	Year Ended Dec. 31
(Millions of Dollars)	2020		2019		2018
Balance at Jan. 1	$	12	$	14	$	13
Purchases	23		27		32
Settlements	(23)		(34)		(42)
Net transactions recorded during the period:
Net (losses) gains recognized as regulatory assets	(5)		5		11
Balance at Dec. 31	$	7	$	12	$	14

Carrying Amount and Fair Value of Long-term Debt

	2020				2019
(Millions of Dollars)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term debt	$	2,764	$	3,381	$	2,420	$	2,706