CONDENSED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 19.9	$ 19.6
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation and amortization	94.4	82.4
Deferred income taxes and investment tax credits, net	1.1	0.4
Allowance for equity funds used during construction	(1.3)	(1.5)
Stock-based compensation expense	0.9	1.0
Regulatory assets	(0.3)	7.3
Regulatory liabilities	(11.7)	(7.0)
Other assets	(0.1)	0.5
Other liabilities	(2.5)	2.2
Change in certain current assets and liabilities:
Accounts receivable and accrued unbilled revenues, net	18.9	26.0
Fuel, materials and supplies inventories	(5.0)	9.1
Fuel recoveries	50.3	(22.8)
Other current assets	(4.5)	(3.9)
Accounts payable	(27.0)	(32.4)
Income taxes payable - parent	0.8	0.5
Other current liabilities	(45.5)	(48.5)
Net cash provided from operating activities	89.0	18.3
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures (less allowance for equity funds used during construction)	(127.2)	(152.9)
Net cash used in investing activities	(127.2)	(152.9)
CASH FLOWS FROM FINANCING ACTIVITIES
Payment of long-term debt	0.0	(250.0)
Changes in advances with parent	38.2	384.6
Net cash provided from financing activities	38.2	134.6
NET CHANGE IN CASH AND CASH EQUIVALENTS	0.0	0.0
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	0.0	0.0
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$ 0.0	$ 0.0