Selected Balance Sheet Data (Tables)

9 Months Ended

Sep. 30, 2019

Balance Sheet Related Disclosures [Abstract]

Accounts Receivable, Net

(Millions of Dollars)	Sept. 30, 2019			Dec. 31, 2018
Accounts receivable, net
Accounts receivable	$	54.0		$	80.7
Less allowance for bad debts	(5.1		)	(5.6		)
Accounts receivable, net	$	48.9		$	75.1

Inventories

(Millions of Dollars)	Sept. 30, 2019		Dec. 31, 2018
Inventories
Materials and supplies	$	7.0	$	6.7
Fuel	4.1		3.8
Natural gas	6.9		6.6
Total inventories	$	18.0	$	17.1

Property, Plant and Equipment, Net

(Millions of Dollars)	Sept. 30, 2019			Dec. 31, 2018
Property, plant and equipment, net
Electric plant	$	2,963.7		$	2,895.5
Natural gas plant	358.9			345.7
Common and other property	199.2			189.7
Construction work in progress	80.1			55.0
Total property, plant and equipment	3,601.9			3,485.9
Less accumulated depreciation	(1,297.6		)	(1,244.3		)
Property, plant and equipment, net	$	2,304.3		$	2,241.6