Selected Balance Sheet Data (Tables)

9 Months Ended

Sep. 30, 2020

Balance Sheet Related Disclosures [Abstract]

Accounts Receivable, Net

(Millions of dollars)	Sept. 30, 2020		Dec. 31, 2019
Accounts receivable, net
Accounts receivable	$	60.3	$	64.7
Less allowance for bad debts	(6.5)		(5.5)
Accounts receivable, net	$	53.8	$	59.2

Inventories

(Millions of dollars)	Sept. 30, 2020		Dec. 31, 2019
Inventories
Materials and supplies	$	7.1	$	6.8
Fuel	4.2		4.0
Natural gas	5.3		5.2
Total inventories	$	16.6	$	16.0

Property, Plant and Equipment, Net

(Millions of dollars)	Sept. 30, 2020		Dec. 31, 2019
Property, plant and equipment, net
Electric plant	$	3,104.3	$	3,024.6
Natural gas plant	383.1		365.5
Common and other property	204.9		201.5
Construction work in progress	136.8		82.8
Total property, plant and equipment	3,829.1		3,674.4
Less accumulated depreciation	(1,376.7)		(1,315.0)
Property, plant and equipment, net	$	2,452.4	$	2,359.4