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Schedule II, Valuation and Qualifying Accounts
 12 Months Ended
Dec. 31, 2019
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]  
Schedule II, Valuation and Qualifying Accounts
Southwestern Public Service Co. Valuation and Qualifying Accounts Years Ended Dec. 31
 
 
Allowance for bad debts
(Millions of Dollars)
 
2019
 
2018
 
2017
Balance at Jan. 1
 
$
5.6

 
$
6.4

 
$
6.4

Additions charged to costs and expenses
 
5.7

 
4.9

 
5.1

Additions charged to other accounts (a)
 
1.5

 
1.0

 
1.2

Deductions from reserves (b)
 
(7.5
)
 
(6.7
)
 
(6.3
)
Balance at Dec. 31
 
$
5.3

 
$
5.6

 
$
6.4

(a) 
Recovery of amounts previously written off.
(b) 
Deductions related primarily to bad debt write-offs.