Fair Value of Financial Assets and Liabilities - Impact of Derivative Activities on Income and Accumulated Other Comprehensive Loss (Details) - USD ($)
$ in Millions

3 Months Ended

Mar. 31, 2025

Mar. 31, 2024

Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]

Derivative instruments designated as fair value hedges

$ 0

Interest Rate Swap [Member]

Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]

Derivative Liability, Notional Amount

Other Derivative Instruments

Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]

FTR settlement gains

(11)

Pre-Tax fair value gains (losses) recognized during the period in

(1)

Other Derivative Instruments | Electric Commodity

Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]

FTR settlement gains

^[1]

(11)

Other Derivative Instruments | Commodity Contract [Member]

Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]

Pre-Tax fair value gains (losses) recognized during the period in

$ 8

$ (1)

[1]

Recorded to electric fuel and purchased power. These derivative settlement gains and losses are shared with electric customers through fuel and purchased energy cost-recovery mechanisms, and reclassified out of income as regulatory assets or liabilities, as appropriate. FTR settlements are shared with customers and do not have a material impact on net income. Presented amounts reflect changes in fair value between auction and settlement dates, but exclude the original auction fair value.

- Definition

Nominal or face amount used to calculate payments on the derivative liability.

+ References + Details

SOUTHWESTERN PUBLIC SERVICE CO 10-Q