CONDENSED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenues from contracts with customers	$ 687.8	$ 739.2	$ 1,600.2	$ 1,717.7
Other revenues	14.3	16.2	36.7	41.4
Operating revenues	702.1	755.4	1,636.9	1,759.1
COST OF SALES	209.1	234.0	481.5	625.3
OPERATING EXPENSES
Other operation and maintenance	110.1	130.0	348.8	370.3
Depreciation and amortization	100.5	94.1	292.2	260.8
Taxes other than income	23.9	22.3	72.8	66.8
Operating expenses	234.5	246.4	713.8	697.9
OPERATING INCOME	258.5	275.0	441.6	435.9
OTHER INCOME (EXPENSE)
Allowance for equity funds used during construction	1.1	1.0	3.7	3.7
Other net periodic benefit expense	(1.3)	(0.7)	(2.8)	(0.3)
Other income	1.1	2.0	3.7	4.5
Other expense	(0.3)	(2.4)	(1.7)	(3.9)
Net other income	0.6	(0.1)	2.9	4.0
INTEREST EXPENSE
Interest on long-term debt	38.7	37.5	114.1	101.9
Allowance for borrowed funds used during construction	(0.5)	(0.6)	(1.5)	(2.2)
Interest on short-term debt and other interest charges	1.3	1.1	3.1	4.0
Interest expense	39.5	38.0	115.7	103.7
INCOME BEFORE TAXES	219.6	236.9	328.8	336.2
INCOME TAX EXPENSE	20.1	9.7	30.5	14.9
NET INCOME	199.5	227.2	298.3	321.3
Other comprehensive income, net of tax	0.0	0.0	0.0	0.0
COMPREHENSIVE INCOME	$ 199.5	$ 227.2	$ 298.3	$ 321.3