Fair Value of Financial Assets and Liabilities - Recurring Fair Value Measurements (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2022		Jun. 30, 2021	Jun. 30, 2022		Jun. 30, 2021	Dec. 31, 2021
Derivatives, Fair Value
Reclaim Cash Collateral		$ 0			$ 0			$ 0
Return Cash Collateral		0			0			0
Commodity Contract [Member]
Changes in Level 3 Commodity Derivatives
Balance at beginning of period		32		$ 12	27		$ 7
Purchases	[1]	232		9	237		9
Settlements	[1]	(85)		(12)	(94)		(21)
Net gains recognized as regulatory assets and liabilities	[1]	105		32	114		46
Balance at end of period		284		41	284		41
Transfers Level 3, Net		0		$ 0	0		$ 0
Other Current Assets
Derivatives, Fair Value
Derivative asset, net		287			287			30
Other Noncurrent Assets
Derivatives, Fair Value
Derivative asset, net		5			5			6
Other Current Liabilities
Derivatives, Fair Value
Derivative liability, net		4			4			4
Other Noncurrent Liabilities
Derivatives, Fair Value
Derivative liability, net		4			4			6
Fair Value Measured on a Recurring Basis | Other Current Assets
Derivatives, Fair Value
Derivative asset, gross		284			284			27
Asset, netting	[2]	0			0			0
Derivative asset, net		284			284			27
Fair Value Measured on a Recurring Basis | Other Current Assets | Level 1
Derivatives, Fair Value
Derivative asset, gross		0			0			0
Fair Value Measured on a Recurring Basis | Other Current Assets | Level 2
Derivatives, Fair Value
Derivative asset, gross		0			0			0
Fair Value Measured on a Recurring Basis | Other Current Assets | Level 3
Derivatives, Fair Value
Derivative asset, gross		284			284			27
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross	[3]	284			284			27
Asset, netting	[2],[3]	0			0			0
Derivative asset, net	[3]	284			284			27
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Level 1 | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross	[3]	0			0			0
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Level 2 | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross	[3]	0			0			0
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Level 3 | Electric Commodity
Derivatives, Fair Value
Derivative asset, gross	[3]	284			284			27
Fair Value, Measurements, Nonrecurring | Other Current Assets | PPAs
Derivatives, Fair Value
Derivative asset, net	[4]	3			3			3
Fair Value, Measurements, Nonrecurring | Other Noncurrent Assets | PPAs
Derivatives, Fair Value
Derivative asset, net	[4]	5			5			6
Fair Value, Measurements, Nonrecurring | Other Current Liabilities | PPAs
Derivatives, Fair Value
Derivative liability, net		4	[4]		4	[4]		4
Fair Value, Measurements, Nonrecurring | Other Noncurrent Liabilities | PPAs
Derivatives, Fair Value
Derivative liability, net		$ 4	[4]		$ 4	[4]		$ 6

[1] Relates primarily to FTR instruments administered by SPP (annual auctions occurring in the second quarter). These instruments are utilized/intended to offset the impacts of transmission system congestion. Higher congestion costs have led to an increase in the fair value of FTRs. Due to regulatory recovery, changes in fair value are deferred as a regulatory asset or liability and do not have a material impact on net income.

[2] 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 June 30, 2022 and Dec. 31, 2021. At June 30, 2022 and Dec. 31, 2021, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. The counterparty netting excludes settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

[3] Amounts relate to FTR instruments administered by SPP (annual auctions occurring in the second quarter). These instruments are utilized/intended to offset the impacts of transmission system congestion. Higher congestion costs have led to an increase in the fair value of FTRs. Due to regulatory recovery, changes in fair value are deferred as a regulatory asset or liability and do not have a material impact on net income.

[4] 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.