Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2025

Commitments and Contingencies Disclosure [Abstract]

Asset Retirement Obligations

	2025
(Millions of Dollars)	Jan. 1, 2025		Accretion		Dec. 31, 2025
Electric
Steam and other production	$	102	$	5	$	107
Wind	55		2		57
Distribution	10		—		10
Total liability	$	167	$	7	$	174

	2024
(Millions of Dollars)	Jan. 1, 2024		Amounts Incurred (a)		Accretion		Cash Flow Revisions		Dec. 31, 2024
Electric
Steam and other production	$	87	$	9	$	5	$	1	$	102
Wind	56		—		2		(3)		55
Distribution	10		—		—		—		10
Total liability	$	153	$	9	$	7	$	(2)	$	167

(a)Amounts incurred pertain to CCR coal ash regulations and the Harrington pipeline which was placed in service in 2024.

Assets and Liabilities, Lessee [Table Text Block]

Operating lease ROU assets:

(Millions of Dollars)	Dec. 31, 2025		Dec. 31, 2024
PPAs	$	500	$	500
Other	44		44
Gross operating lease ROU assets	544		544
Accumulated amortization	(207)		(173)
Net operating lease ROU assets	$	337	$	371

Lessee, Operating Lease, Liability, Maturity [Table Text Block]

Commitments under operating leases as of Dec. 31, 2025:

(Millions of Dollars)	PPA (a) (b) Operating Leases		Other Operating Leases		Total Operating Leases
2026	$	46	$	3	$	49
2027	46		3		49
2028	46		4		50
2029	46		4		50
2030	46		4		50
Thereafter	128		25		153
Total minimum obligation	358		43		401
Interest component of obligation	(55)		(9)		(64)
Present value of minimum obligation	303		34		337
Less current portion					(36)
Noncurrent operating lease liabilities					$	301
Weighted-average remaining lease term in years					8.1

(a)Amounts do not include PPAs accounted for as executory contracts and/or contingent payments, such as energy payments on renewable PPAs.

(b)PPA operating leases contractually expire at various dates through 2033.

PPA operating lease payments are included in electric fuel and purchased power, and expense for other operating leases is included in O&M expense and electric fuel and purchased power.

Components of lease expense:

(Millions of Dollars)	2025		2024		2023
Operating leases
PPA capacity payments	$	39	$	48	$	53
Other operating leases (a)	4		3		4
Total operating lease expense	$	43	$	51	$	57

(a)Includes immaterial short-term lease expense.

^[1]

Estimated Future Payments for Capacity and Energy Pursuant to Purchased Power Agreements

At Dec. 31, 2025, the estimated future payments for capacity and energy that SPS is obligated to purchase pursuant to these executory contracts, subject to availability, were as follows:

(Millions of Dollars)	Capacity		Energy (a)
2026	$	16	$	44
2027	17		46
2028	18		45
2029	19		43
2030	20		42
Thereafter	204		411
Total	$	294	$	631

(a)Excludes contingent energy payments for renewable energy PPAs.

Estimated Minimum Purchases Under Fuel Contracts

Estimated minimum purchases under these contracts as of Dec. 31, 2025:

(Millions of Dollars)	Coal		Natural gas supply		Natural gas storage and transportation
2026	$	75	$	26	$	67
2027	62		—		66
2028	—		—		57
2029	—		—		36
2030	—		—		11
Thereafter	—		—		40
Total	$	137	$	26	$	277

[1] Amounts do not include PPAs accounted for as executory contracts and/or contingent payments, such as energy payments on renewable PPAs.