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Commitments and Contingencies (Tables)
 12 Months Ended
Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]  
Asset Retirement Obligations
NSP-Wisconsin’s AROs were as follows:
2024
(Millions of Dollars)Jan. 1, 2024Amounts IncurredDec. 31, 2024
Electric
Steam, hydro and other production$9 $1 $10 
Distribution5 — 5 
Natural gas
Distribution8 — 8 
Total liability (a)
$22 $1 $23 
(a)Included in other long-term liabilities balance in the consolidated balance sheet.
2023
(Millions of Dollars)Jan. 1, 2023Accretion
Cash Flow Revisions (a)
Dec. 31, 2023
Electric
Steam, hydro and other production$10 $— $(1)$9 
Distribution5 — — 5 
Natural gas
Distribution13 1 (6)8 
Total liability (b)
$28 $1 $(7)$22 
(a)In 2023, AROs were revised for changes in timing and estimates of cash flows. Changes in gas distribution AROs were a result of updated mileage of gas lines and number of services, as well as changes to inflation and discount rate assumptions.
(b)Included in other long-term liabilities balance in the consolidated balance sheet.
Estimated Minimum Purchases Under Fuel Contracts
Estimated minimum purchases under these contracts as of Dec. 31, 2024:
(Millions of Dollars)RDF/woodNatural gas
supply		Natural gas
storage and
transportation
2025$5 $12 $21 
20261 — 22 
20271 — 16 
20281 — 7 
20291 — 6 
Thereafter1 — 15 
Total (a)
$10 $12 $87 
(a)Excludes additional amounts allocated from NSP-Minnesota through interchange billings.
Estimated Minimum Purchases Under Fuel Contracts
(Millions of Dollars)RDF/woodNatural gas
supply		Natural gas
storage and
transportation
2025$5 $12 $21 
20261 — 22 
20271 — 16 
20281 — 7 
20291 — 6 
Thereafter1 — 15 
Total (a)
$10 $12 $87