CONDENSED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenues from contracts with customers	$ 492.0	$ 501.1	$ 912.4	$ 978.5
Other revenues	11.5	12.6	22.4	25.2
Operating revenues	503.5	513.7	934.8	1,003.7
COST OF SALES	137.4	178.7	272.4	391.3
OPERATING EXPENSES
Other operation and maintenance	117.7	120.0	238.7	240.3
Depreciation and amortization	97.3	84.3	191.7	166.7
Taxes other than income	25.0	20.1	48.9	44.5
Operating expenses	240.0	224.4	479.3	451.5
OPERATING INCOME	126.1	110.6	183.1	160.9
OTHER INCOME (EXPENSE)
Allowance for equity funds used during construction	1.3	1.2	2.6	2.7
Other net periodic benefit income (expense)	(1.0)	0.0	(1.5)	0.4
Other income	1.1	1.1	2.6	2.5
Other expense	(0.9)	(0.8)	(1.4)	(1.5)
Net other income	0.5	1.5	2.3	4.1
INTEREST EXPENSE
Interest on long-term debt	38.8	31.8	75.4	64.4
Allowance for borrowed funds used during construction	(0.5)	(0.6)	(1.0)	(1.6)
Interest on short-term debt and other interest charges	1.0	2.1	1.8	2.9
Interest expense	39.3	33.3	76.2	65.7
INCOME BEFORE TAXES	87.3	78.8	109.2	99.3
INCOME TAX EXPENSE	8.4	4.3	10.4	5.2
NET INCOME	78.9	74.5	98.8	94.1
Other comprehensive income, net of tax	0.0	0.0	0.0	0.0
COMPREHENSIVE INCOME	$ 78.9	$ 74.5	$ 98.8	$ 94.1