CONDENSED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Revenues from contracts with customers	$ 420.4	$ 477.4
Other revenues	10.9	12.6
Operating revenues	431.3	490.0
COST OF SALES	135.0	212.6
OPERATING EXPENSES
Other operation and maintenance	121.0	120.3
Depreciation and amortization	94.4	82.4
Taxes other than income	23.9	24.4
Operating expenses	239.3	227.1
OPERATING INCOME	57.0	50.3
OTHER INCOME (EXPENSE)
Allowance for equity funds used during construction	1.3	1.5
Other net periodic benefit income (expense)	(0.5)	0.4
Other income	1.5	1.4
Other expense	(0.5)	(0.7)
Net other income	1.8	2.6
INTEREST EXPENSE
Interest on long-term debt	36.6	32.6
Allowance for borrowed funds used during construction	(0.5)	(1.0)
Interest on short-term debt and other interest charges	0.8	0.8
Interest expense	36.9	32.4
INCOME BEFORE TAXES	21.9	20.5
INCOME TAX EXPENSE	2.0	0.9
NET INCOME	19.9	19.6
Other comprehensive income, net of tax	0.0	0.0
COMPREHENSIVE INCOME	$ 19.9	$ 19.6