CONDENSED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 298.3	$ 321.3
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation and amortization	292.2	260.8
Deferred income taxes and investment tax credits, net	23.9	8.7
Allowance for equity funds used during construction	(3.7)	(3.7)
Stock-based compensation expense	2.2	3.7
Regulatory assets	(8.5)	(48.1)
Regulatory liabilities	(48.6)	(32.1)
Other assets	(3.2)	2.8
Other liabilities	(27.6)	1.1
Change in certain current assets and liabilities:
Accounts receivable and accrued unbilled revenues, net	(62.4)	(78.6)
Fuel, materials and supplies inventories	(2.0)	8.0
Fuel recoveries	74.3	(44.8)
Other current assets	(5.8)	8.9
Accounts payable	(59.6)	(54.1)
Income taxes payable - parent	9.6	2.6
Other current liabilities	(0.7)	(13.1)
Net cash provided from operating activities	478.4	343.4
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures (less allowance for equity funds used during construction)	(419.7)	(476.5)
Net cash used in investing activities	(419.7)	(476.5)
CASH FLOWS FROM FINANCING ACTIVITIES
Dividends paid on common stock	(75.0)	0.0
Proceeds from long-term debt	297.1	296.4
Payment of long-term debt	(0.1)	(250.0)
Changes in advances with parent	(248.7)	99.9
Net cash provided from (used in) financing activities	(26.7)	146.3
NET CHANGE IN CASH AND CASH EQUIVALENTS	32.0	13.2
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	0.0	0.0
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$ 32.0	$ 13.2