CONDENSED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Revenues from contracts with customers	$ 501.1	$ 547.7	$ 978.5	$ 1,025.6
Other revenues	12.6	19.3	25.2	34.1
Operating revenues	513.7	567.0	1,003.7	1,059.7
COST OF SALES	178.7	208.7	391.3	419.2
OPERATING EXPENSES
Other operation and maintenance	120.0	117.5	240.3	231.1
Depreciation and amortization	84.3	80.9	166.7	159.7
Taxes other than income	20.1	21.6	44.5	44.3
Operating expenses	224.4	220.0	451.5	435.1
OPERATING INCOME	110.6	138.3	160.9	205.4
OTHER INCOME (EXPENSE)
Allowance for equity funds used during construction	1.2	6.3	2.7	13.3
Other net periodic benefit income (expense)	0.0	(5.2)	0.4	(10.0)
Other income	1.1	3.5	2.5	6.6
Other expense	(0.8)	(0.6)	(1.5)	(1.4)
Net other income	1.5	4.0	4.1	8.5
INTEREST EXPENSE
Interest on long-term debt	31.8	39.7	64.4	79.3
Allowance for borrowed funds used during construction	(0.6)	(2.8)	(1.6)	(6.5)
Interest on short-term debt and other interest charges	2.1	2.3	2.9	3.7
Interest expense	33.3	39.2	65.7	76.5
INCOME BEFORE TAXES	78.8	103.1	99.3	137.4
INCOME TAX EXPENSE	4.3	11.1	5.2	14.1
NET INCOME	74.5	92.0	94.1	123.3
Other comprehensive income, net of tax	0.0	0.0	0.0	0.0
COMPREHENSIVE INCOME	$ 74.5	$ 92.0	$ 94.1	$ 123.3