CONDENSED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 98.8	$ 94.1
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation and amortization	191.7	166.7
Deferred income taxes and investment tax credits, net	6.7	(6.2)
Allowance for equity funds used during construction	(2.6)	(2.7)
Stock-based compensation expense	1.6	2.0
Regulatory assets	(6.1)	(25.6)
Regulatory liabilities	(26.7)	(21.1)
Other assets	(2.3)	1.5
Other liabilities	(7.0)	(0.5)
Change in certain current assets and liabilities:
Accounts receivable and accrued unbilled revenues, net	(34.2)	(13.8)
Fuel, materials and supplies inventories	(1.5)	7.2
Fuel recoveries	71.9	(28.9)
Other current assets	(6.8)	(1.1)
Accounts payable	(45.6)	(74.1)
Income taxes payable - parent	5.0	7.7
Other current liabilities	(19.0)	(31.2)
Net cash provided from operating activities	223.9	74.0
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures (less allowance for equity funds used during construction)	(280.8)	(314.5)
Net cash used in investing activities	(280.8)	(314.5)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from Issuance of Long-term Debt	297.2	295.9
Payment of long-term debt	0.0	(250.0)
Changes in advances with parent	(172.8)	194.6
Net cash provided from financing activities	124.4	240.5
NET CHANGE IN CASH AND CASH EQUIVALENTS	67.5	0.0
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	0.0	0.0
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$ 67.5	$ 0.0