STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues [Abstract]
Operating revenues	$ 454.1	$ 447.2
Operating expenses
Electric fuel and purchased power	230.9	253.9
Operating and maintenance expenses	72.4	66.1
Demand side management expenses	4.6	4.1
Depreciation and amortization	53.2	48.4
Taxes (other than income taxes)	18.5	17.6
Total operating expenses	379.6	390.1
Operating income	74.5	57.1
Other income (expense), net	(0.4)	(0.7)
Allowance for funds used during construction — equity	10.3	3.4
Interest charges and financing costs
Interest charges — includes other financing costs of $0.8 and $0.7 respectively	24.4	20.2
Allowance for funds used during construction — debt	(4.5)	(1.8)
Total interest charges and financing costs	19.9	18.4
Income before income taxes	65.3	41.4
Income taxes	11.2	8.3
Net income	$ 54.1	$ 33.1