Fair Value of Financial Assets and Liabilities - Recurring Fair Value Measurements (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Changes in Level 3 Commodity Derivatives
Derivative instruments designated as fair value hedges		$ 0		$ 0
External credit rating, investment grade | Credit Concentration Risk
Changes in Level 3 Commodity Derivatives
Credit exposure, percentage		30.00%		30.00%
Commodity Contract [Member]
Changes in Level 3 Commodity Derivatives
Balance at beginning of period		$ 83	$ 284	$ 119	$ 27
Purchases	[1]	1	4	75	241
Settlements	[1]	(18)	(22)	(66)	(116)
Net gains recognized as regulatory assets and liabilities	[1]	(3)	(32)	(65)	82
Balance at end of period		63	$ 234	63	$ 234
Other Current Assets
Derivatives, Fair Value
Derivative asset, net		66		66		$ 122
Other Noncurrent Assets
Derivatives, Fair Value
Derivative asset, net		1		1		3
Other Current Liabilities
Derivatives, Fair Value
Derivative liability, net		4		4		4
Other Noncurrent Liabilities
Derivatives, Fair Value
Derivative liability, net		0		0		2
Fair Value Measured on a Recurring Basis
Derivatives, Fair Value
Derivative asset, gross		63		63		119
Asset, netting	[2]	0		0		0
Derivative asset, net		63		63		119
Fair Value Measured on a Recurring Basis | Level 1
Derivatives, Fair Value
Derivative asset, gross		0		0		0
Fair Value Measured on a Recurring Basis | Level 2
Derivatives, Fair Value
Derivative asset, gross		0		0		0
Fair Value Measured on a Recurring Basis | Level 3
Derivatives, Fair Value
Derivative asset, gross		63		63		119
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross		63		63		119
Asset, netting	[2]	0		0		0
Derivative asset, net		63		63		119
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Level 1 | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross		0		0		0
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Level 2 | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross		0		0		0
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Level 3 | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross		63		63		119
Fair Value, Measurements, Nonrecurring | Other Current Assets | PPAs
Derivatives, Fair Value
Derivative asset, net	[3]	3		3		3
Fair Value, Measurements, Nonrecurring | Other Noncurrent Assets | PPAs
Derivatives, Fair Value
Derivative asset, net	[3]	1		1		3
Fair Value, Measurements, Nonrecurring | Other Current Liabilities | PPAs
Derivatives, Fair Value
Derivative liability, net	[3]	4		4		4
Fair Value, Measurements, Nonrecurring | Other Noncurrent Liabilities | PPAs
Derivatives, Fair Value
Derivative liability, net	[3]	$ 0		$ 0		$ 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 Sept. 30, 2023 and Dec. 31, 2022, 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.