Selected Balance Sheet Data (Tables)

3 Months Ended

Mar. 31, 2019

Balance Sheet Related Disclosures [Abstract]

Accounts Receivable, Net

(Millions of Dollars)	March 31, 2019			Dec. 31, 2018
Accounts receivable, net
Accounts receivable	$	78.5		$	80.7
Less allowance for bad debts	(5.6		)	(5.6		)
	$	72.9		$	75.1

Inventories

(Millions of Dollars)	March 31, 2019		Dec. 31, 2018
Inventories
Materials and supplies	$	7.0	$	6.7
Fuel	3.6		3.8
Natural gas	1.1		6.6
	$	11.7	$	17.1

Property, Plant and Equipment, Net

(Millions of Dollars)	March 31, 2019			Dec. 31, 2018
Property, plant and equipment, net
Electric plant	$	2,910.1		$	2,895.5
Natural gas plant	348.3			345.7
Common and other property	188.6			189.7
Construction work in progress	66.5			55.0
Total property, plant and equipment	3,513.5			3,485.9
Less accumulated amortization	(1,264.1		)	(1,244.3		)
	$	2,249.4		$	2,241.6