CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Electric, Non-affiliate	$ 170.9	$ 170.9
Electric, affiliates	40.9	44.1
Natural gas	45.2	61.1
Other	0.0	0.1
Total operating revenues	257.0	276.2
Operating expenses
Electric Fuel and Purchased Power, Non-Affiliate	2.9	1.9
Related Party Transaction, Utilities Operating Expense, Purchased Power	94.3	103.5
Cost of Goods Sold	21.4	32.3
Operating and maintenance expenses	48.6	52.0
Conservation program expenses	3.1	3.0
Depreciation and amortization	38.6	34.0
Taxes (other than income taxes)	7.0	7.5
Total operating expenses	215.9	234.2
Operating income	41.1	42.0
Other expense, net	(2.5)	(0.4)
Allowance for funds used during construction — equity	1.1	0.6
Interest charges and financing costs
Interest charges — includes other financing costs of $0.3 and $0.3, respectively	9.9	10.0
Allowance for funds used during construction — debt	(0.5)	(0.3)
Total interest charges and financing costs	9.4	9.7
Income before income taxes	30.3	32.5
Income tax (benefit) expense	(3.3)	8.5
Net income	$ 33.6	$ 24.0