Selected Balance Sheet Data (Tables)

6 Months Ended

Jun. 30, 2019

Balance Sheet Related Disclosures [Abstract]

Accounts Receivable, Net

(Millions of Dollars)	June 30, 2019			Dec. 31, 2018
Accounts receivable, net
Accounts receivable	$	58.2		$	80.7
Less allowance for bad debts	(4.6		)	(5.6		)
	$	53.6		$	75.1

Inventories

(Millions of Dollars)	June 30, 2019		Dec. 31, 2018
Inventories
Materials and supplies	$	7.1	$	6.7
Fuel	3.8		3.8
Natural gas	3.1		6.6
	$	14.0	$	17.1

Property, Plant and Equipment, Net

(Millions of Dollars)	June 30, 2019			Dec. 31, 2018
Property, plant and equipment, net
Electric plant	$	2,933.3		$	2,895.5
Natural gas plant	351.2			345.7
Common and other property	197.2			189.7
Construction work in progress	63.0			55.0
Total property, plant and equipment	3,544.7			3,485.9
Less accumulated depreciation	(1,281.7		)	(1,244.3		)
	$	2,263.0		$	2,241.6