Fair Value of Financial Assets and Liabilities - Recurring Fair Value Measurements (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Derivatives, Fair Value
Return Cash Collateral		$ 0		$ 0
Changes in Level 3 Commodity Derivatives
Derivative instruments designated as fair value hedges		0	$ 0
Derivative Asset, Current		$ 47		$ 42
Derivative Asset, Current, Statement of Financial Position [Extensible Enumeration]		Assets, Current		Assets, Current
Derivative Liability, Noncurrent		$ 1		$ 2
External credit rating, investment grade | Credit Concentration Risk
Changes in Level 3 Commodity Derivatives
Credit exposure, percentage		15.00%
Commodity Contract [Member]
Changes in Level 3 Commodity Derivatives
Balance at beginning of period		$ 39	119
Purchases	[1]	3	6
Settlements	[1]	(36)	(16)
Net gains recognized as regulatory assets and liabilities	[1]	46	(86)
Balance at end of period		52	$ 23
Fair Value Measured on a Recurring Basis
Derivatives, Fair Value
Derivative asset, gross		45		39
Asset, netting	[2]	0		0
Changes in Level 3 Commodity Derivatives
Derivative Asset, Current		45		39
Derivative Asset, Noncurrent		7		0
Fair Value Measured on a Recurring Basis | Level 1
Derivatives, Fair Value
Derivative asset, gross		0		0
Fair Value Measured on a Recurring Basis | Level 2
Derivatives, Fair Value
Derivative asset, gross		0		0
Fair Value Measured on a Recurring Basis | Level 3
Derivatives, Fair Value
Derivative asset, gross		45		39
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross		45		39
Asset, netting	[2]	0		0
Changes in Level 3 Commodity Derivatives
Derivative Asset, Current		45		39
Derivative Asset, Noncurrent		7		0
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Level 1 | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross		0		0
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Level 2 | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross		0		0
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Level 3 | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross		45		39
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets
Derivatives, Fair Value
Derivative asset, gross		0		0
Asset, netting		0		0
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Level 1
Derivatives, Fair Value
Derivative asset, gross		0		0
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Level 2
Derivatives, Fair Value
Derivative asset, gross		0		0
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Level 3
Derivatives, Fair Value
Derivative asset, gross		7		0
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross		0		0
Asset, netting		0		0
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Level 1 | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross		0		0
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Level 2 | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross		0		0
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Level 3 | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross		7		0
Fair Value, Measurements, Nonrecurring | PPAs
Changes in Level 3 Commodity Derivatives
Derivative Asset, Current	[3]	2		3
Derivative Liability, Noncurrent	[3]	$ 1		$ 2

[1] Relates primarily to FTR instruments administered by SPP.

[2] SPS nets derivative instruments and related collateral on its balance sheet when supported by a legally enforceable master netting agreement. At March 31, 2024 and Dec. 31, 2023, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral.

[3] SPS currently applies the normal purchase exception to qualifying PPAs. Balance relates to specific contracts that were previously recognized at fair value prior to applying the normal purchase exception, and are being amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.