Benefit Plans and Other Postretirement Benefits, Pension Plan Benefit Obligations, Cash Flows and Benefit Costs (Details)	1 Months Ended		12 Months Ended
	Jan. 31, 2025 USD ($)		Dec. 31, 2026 USD ($)		Dec. 31, 2025 USD ($) Plan		Dec. 31, 2024 USD ($)		Dec. 31, 2023 USD ($)
Funded Status of Plans at Dec. 31 [Abstract]
Liability, Defined Benefit Plan, Noncurrent					$ (12,000,000)		$ (17,000,000)
Significant Assumptions Used to Measure Costs [Abstract]
annual interest crediting rates					4.82		4.84		4.45
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated Benefit Obligation at Dec. 31					$ 393,000,000		$ 383,000,000
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1	$ 409,000,000		$ 420,000,000		409,000,000		425,000,000
Service cost					7,000,000		7,000,000		$ 7,000,000
Interest cost					23,000,000		22,000,000		22,000,000
Actuarial loss					12,000,000		(12,000,000)
Plan participant's contributions					0		0
Benefit payments					(31,000,000)		(33,000,000)
Obligation at Dec. 31					420,000,000		409,000,000		425,000,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1	397,000,000	[1]	413,000,000	[1]	397,000,000	[1]	420,000,000
Actual return on plan assets					44,000,000		7,000,000
Employer contributions					3,000,000		3,000,000
Benefit payments					(31,000,000)		(33,000,000)
Fair value of plan assets at Dec. 31					413,000,000	[1]	397,000,000	[1]	420,000,000
Funded Status of Plans at Dec. 31 [Abstract]
Funded status					(7,000,000)		(12,000,000)
Liability, Defined Benefit Plan, Noncurrent					(7,000,000)		(12,000,000)
Assets for Plan Benefits, Defined Benefit Plan					0		0
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery Rates [Abstract]
Net loss					162,000,000		165,000,000
Prior service credit					(1,000,000)		(1,000,000)
Total					161,000,000		164,000,000
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Current regulatory assets					5,000,000		4,000,000
Noncurrent regulatory assets					156,000,000		160,000,000
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Liabilities					0		0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Liabilities					0		0
Total					$ 161,000,000		$ 164,000,000
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Discount rate for year-end valuation (as a percent)					5.78%		5.88%
Expected average long-term increase in compensation level (as a percent)					4.25%		4.25%
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost					$ 7,000,000		$ 7,000,000		7,000,000
Interest cost					23,000,000		22,000,000		22,000,000
Expected return on plan assets					(32,000,000)		(32,000,000)		(32,000,000)
Amortization of net loss					3,000,000		3,000,000		2,000,000
Net periodic pension cost					1,000,000		0		(1,000,000)
Net benefit cost recognized for financial reporting					$ 3,000,000		$ (1,000,000)		$ 4,000,000
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (as a percent)					5.88%		5.49%		5.80%
Expected average long-term increase in compensation level (as a percent)					4.25%		4.25%		4.25%
Expected average long-term rate of return on assets (as a percent)					7.03%		6.97%		6.96%
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position					$ (7,000,000)		$ (12,000,000)
Defined Benefit Plan, Costs Not Recognized Due To Regulation					2,000,000		(1,000,000)		$ 5,000,000
Pension Plan [Member] | SPS [Member]
Cash Flows [Abstract]
Payment for Pension Benefits	2,000,000				3,000,000		3,000,000
Pension Plan [Member] | Xcel Energy [Member]
Cash Flows [Abstract]
Payment for Pension Benefits	75,000,000				125,000,000		100,000,000		50,000,000
Other Postretirement Benefits Plan [Member]
Change in Projected Benefit Obligation [Roll Forward]
Obligation at Jan. 1	26,000,000		30,000,000		26,000,000		26,000,000
Service cost					1,000,000		1,000,000		1,000,000
Interest cost					1,000,000		1,000,000		1,000,000
Actuarial loss					4,000,000		1,000,000
Plan participant's contributions					0		1,000,000
Benefit payments					(2,000,000)		(4,000,000)
Obligation at Dec. 31					30,000,000		26,000,000		26,000,000
Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1	$ 36,000,000	[2]	37,000,000	[2]	36,000,000	[2]	36,000,000
Actual return on plan assets					3,000,000		2,000,000
Employer contributions					0		1,000,000
Benefit payments					(2,000,000)		(4,000,000)
Fair value of plan assets at Dec. 31					37,000,000	[2]	36,000,000	[2]	36,000,000
Funded Status of Plans at Dec. 31 [Abstract]
Funded status					7,000,000		10,000,000
Liability, Defined Benefit Plan, Noncurrent					0		0
Assets for Plan Benefits, Defined Benefit Plan					7,000,000		10,000,000
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery Rates [Abstract]
Net loss					(15,000,000)		(19,000,000)
Prior service credit					0		0
Total					(15,000,000)		(19,000,000)
Amounts Not Yet Recognized as Components of Net Periodic Benefit Cost Have Been Recorded as Follows Based Upon Expected Recovery in Rates [Abstract]
Current regulatory assets					0		0
Noncurrent regulatory assets					0		0
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Current Regulatory Liabilities					0		(1,000,000)
Amounts Not Yet Recognized As Components Of Net Periodic Benefit Cost Recorded As Noncurrent Regulatory Liabilities					(15,000,000)		(18,000,000)
Total					$ (15,000,000)		$ (19,000,000)
Significant Assumptions Used to Measure Benefit Obligations [Abstract]
Discount rate for year-end valuation (as a percent)					5.66%		5.88%
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost					$ 1,000,000		$ 1,000,000		1,000,000
Interest cost					1,000,000		1,000,000		1,000,000
Expected return on plan assets					(2,000,000)		(2,000,000)		(1,000,000)
Amortization of net loss					(1,000,000)		0		0
Net periodic pension cost					(1,000,000)		0		1,000,000
Net benefit cost recognized for financial reporting					$ (1,000,000)		$ 0		$ 1,000,000
Significant Assumptions Used to Measure Costs [Abstract]
Discount rate (as a percent)					5.88%		5.54%		5.80%
Expected average long-term increase in compensation level (as a percent)					0.00%		0.00%		0.00%
Expected average long-term rate of return on assets (as a percent)					6.25%		5.00%		5.00%
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position					$ 7,000,000		$ 10,000,000
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Pre-65					7.00%		7.00%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Post-65					7.50%		7.50%
Ultimate health care trend assumption rate (as a percent)					4.50%		4.50%
Period until ultimate trend rate is reached (in years)					$ 8		$ 9
Defined Benefit Plan, Costs Not Recognized Due To Regulation					0		0		$ 0
Defined Benefit Plan, Overfunded Plan [Member] | Xcel Energy [Member]
Cash Flows [Abstract]
Payment for Pension Benefits					$ 13,000,000		$ 11,000,000		$ 11,000,000
Subsequent Event | Defined Benefit Plan, Overfunded Plan [Member] | Xcel Energy [Member]
Cash Flows [Abstract]
Payment for Pension Benefits			$ 8,000,000
Parent Company [Member] | Pension Plan [Member]
Cash Flows [Abstract]
Number of pension plans to which contributions were made | Plan					4

[1] See Note 8 for further information on fair value measurement inputs and methods.

[2] See Note 8 for further information on fair value measurement inputs and methods.