Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2024

Commitments and Contingencies Disclosure [Abstract]

Asset Retirement Obligations

	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.

	2023
(Millions of Dollars)	Jan. 1, 2023		Accretion		Dec. 31, 2023
Electric
Steam and other production	$	83	$	4	$	87
Wind	54		2		56
Distribution	10		—		10
Total liability	$	147	$	6	$	153

Assets and Liabilities, Lessee [Table Text Block]

Operating lease ROU assets:

(Millions of Dollars)	Dec. 31, 2024		Dec. 31, 2023
PPAs	$	500	$	500
Other	44		44
Gross operating lease ROU assets	544		544
Accumulated amortization	(173)		(141)
Net operating lease ROU assets	$	371	$	403

Lease, Cost [Table Text Block]

Components of lease expense:

(Millions of Dollars)	2024		2023		2022
Operating leases
PPA capacity payments	$	48	$	53	$	53
Other operating leases (a)	3		4		4
Total operating lease expense (b)	$	51	$	57	$	57

(a)Includes immaterial short-term lease expense for 2024, 2023 and 2022.

(b)PPA capacity payments are included in electric fuel and purchased power on the statements of income. Expense for other operating leases is included in O&M expense.

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

Commitments under operating leases as of Dec. 31, 2024:

(Millions of Dollars)	PPA (a) (b) Operating Leases		Other Operating Leases		Total Operating Leases
2025	$	46	$	3	$	49
2026	46		3		49
2027	46		3		49
2028	46		4		50
2029	46		4		50
Thereafter	174		29		203
Total minimum obligation	404		46		450
Interest component of obligation	(69)		(10)		(79)
Present value of minimum obligation	335		36		371
Less current portion					(34)
Noncurrent operating and finance lease liabilities					$	337
Weighted-average remaining lease term in years					9.1

(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.

^[1]

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

At Dec. 31, 2024, 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)
2025	$	16	$	40
2026	16		38
2027	—		—
2028	—		—
2029	—		—
Thereafter	—		—
Total	$	32	$	78

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

Amounts exclude approximately $1 billion of incremental payments related to SPS’ renegotiation and extension of a non-lease PPA that received PUCT approval in February 2025. The extension to 2040 will result in annual payments of approximately $65 million to $80 million commencing in 2025.

Estimated Minimum Purchases Under Fuel Contracts

Estimated minimum purchases under these contracts as of Dec. 31, 2024:

(Millions of Dollars)	Coal		Natural gas supply		Natural gas storage and transportation
2025	$	75	$	57	$	58
2026	43		—		58
2027	30		—		58
2028	1		—		52
2029	—		—		36
Thereafter	—		—		8
Total	$	149	$	57	$	270

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