CONDENSED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenues from contracts with customers	$ 739.2	$ 684.5	$ 1,717.7	$ 1,710.1
Other revenues	16.2	14.3	41.4	48.4
Operating revenues	755.4	698.8	1,759.1	1,758.5
COST OF SALES	234.0	244.4	625.3	663.6
OPERATING EXPENSES
Other operation and maintenance	130.0	121.1	370.3	352.2
Depreciation and amortization	94.1	81.1	260.8	240.8
Taxes other than income	22.3	21.9	66.8	66.2
Operating expenses	246.4	224.1	697.9	659.2
OPERATING INCOME	275.0	230.3	435.9	435.7
OTHER INCOME (EXPENSE)
Allowance for equity funds used during construction	1.0	6.7	3.7	20.0
Other net periodic benefit income (expense)	(0.7)	0.5	(0.3)	(9.5)
Other income	2.0	3.6	4.5	10.2
Other expense	(2.4)	(0.6)	(3.9)	(2.0)
Net other income (expense)	(0.1)	10.2	4.0	18.7
INTEREST EXPENSE
Interest on long-term debt	37.5	40.2	101.9	119.5
Allowance for borrowed funds used during construction	(0.6)	(3.3)	(2.2)	(9.8)
Interest on short-term debt and other interest charges	1.1	0.9	4.0	4.6
Interest expense	38.0	37.8	103.7	114.3
INCOME BEFORE TAXES	236.9	202.7	336.2	340.1
INCOME TAX EXPENSE	9.7	18.8	14.9	32.9
NET INCOME	227.2	183.9	321.3	307.2
Other comprehensive income, net of tax	0.0	0.0	0.0	0.0
COMPREHENSIVE INCOME	$ 227.2	$ 183.9	$ 321.3	$ 307.2