STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues [Abstract]
Operating revenues	$ 410.5	$ 481.3	$ 864.6	$ 928.6
Operating expenses
Electric fuel and purchased power	179.9	257.6	410.8	511.6
Operating and maintenance expenses	70.1	66.1	142.5	132.2
Demand side management expenses	3.8	4.8	8.4	8.9
Depreciation and amortization	57.8	49.6	111.0	98.0
Taxes (other than income taxes)	17.0	15.6	35.5	33.3
Total operating expenses	328.6	393.7	708.2	784.0
Operating income	81.9	87.6	156.4	144.6
Other income (expense), net	0.5	(0.8)	0.9	(1.5)
Allowance for funds used during construction — equity	8.7	3.2	19.0	6.6
Interest charges and financing costs
Interest charges — includes other financing costs of $0.8, $0.7, $1.6 and $1.4 respectively	25.6	20.6	50.0	40.7
Allowance for funds used during construction — debt	(4.2)	(1.5)	(8.7)	(3.3)
Total interest charges and financing costs	21.4	19.1	41.3	37.4
Income before income taxes	69.7	70.9	135.0	112.3
Income taxes	10.9	12.4	22.1	20.7
Net income	$ 58.8	$ 58.5	$ 112.9	$ 91.6