CONDENSED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenues from contracts with customers	$ 684.5	$ 0.0	$ 1,710.1	$ 0.0
Other revenues	14.3	0.0	48.4	0.0
Operating revenues	698.8	716.8	1,758.5	1,759.2
COST OF SALES	244.4	255.7	663.6	696.5
OPERATING EXPENSES
Other operation and maintenance	121.1	115.0	352.2	348.8
Depreciation and amortization	81.1	76.2	240.8	204.6
Taxes other than income	21.9	21.7	66.2	64.2
Operating expenses	224.1	212.9	659.2	617.6
OPERATING INCOME	230.3	248.2	435.7	445.1
OTHER INCOME (EXPENSE)
Allowance for equity funds used during construction	6.7	11.8	20.0	27.2
Other net periodic benefit income (expense)	0.5	(5.2)	(9.5)	(14.0)
Other income	3.6	13.4	10.2	27.5
Other expense	(0.6)	(0.5)	(2.0)	(1.5)
Net other income	10.2	19.5	18.7	39.2
INTEREST EXPENSE
Interest on long-term debt	40.2	38.3	119.5	112.4
Allowance for borrowed funds used during construction	(3.3)	(5.2)	(9.8)	(12.6)
Interest on short-term debt and other interest charges	0.9	1.4	4.6	3.9
Interest expense	37.8	34.5	114.3	103.7
INCOME BEFORE TAXES	202.7	233.2	340.1	380.6
INCOME TAX EXPENSE	18.8	71.7	32.9	116.7
NET INCOME	183.9	161.5	307.2	263.9
Other comprehensive income (loss), net of tax	0.0	0.0	0.0	0.0
COMPREHENSIVE INCOME	$ 183.9	$ 161.5	$ 307.2	$ 263.9