CONDENSED BALANCE SHEETS (Unaudited) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
CURRENT ASSETS
Cash and Cash Equivalents, at Carrying Value	$ 32.0	$ 0.0
Accounts receivable, less reserve of $2.6 and $1.5, respectively	209.0	153.8
Accrued unbilled revenues	71.9	64.7
Advances to parent	293.9	304.8
Fuel inventories	36.5	46.3
Materials and supplies, at average cost	107.0	90.6
Fuel clause under recoveries	0.0	39.5
Other	25.4	19.6
Total current assets	775.7	719.3
OTHER PROPERTY AND INVESTMENTS	4.4	4.7
PROPERTY, PLANT AND EQUIPMENT
In service	13,109.1	12,765.0
Construction work in progress	128.9	141.6
Total property, plant and equipment	13,238.0	12,906.6
Less: accumulated depreciation	4,010.1	3,868.1
Net property, plant and equipment	9,227.9	9,038.5
DEFERRED CHARGES AND OTHER ASSETS
Regulatory assets	301.6	306.0
Other	13.7	8.1
Total deferred charges and other assets	315.3	314.1
TOTAL ASSETS	10,323.3	10,076.6
Liabilities, Current [Abstract]
Accounts payable	112.4	175.0
Customer deposits	82.4	83.0
Accrued taxes	70.7	41.9
Accrued interest	40.4	37.9
Accrued compensation	24.4	29.5
Fuel clause over recoveries	39.6	4.8
Other	38.8	65.1
Total current liabilities	408.7	437.2
Long-term Debt, Excluding Current Maturities	3,493.9	3,195.2
Liabilities, Other than Long-term Debt, Noncurrent [Abstract]
Accrued benefit obligations	115.0	133.3
Deferred income taxes	996.2	951.4
Deferred investment tax credits	10.2	7.1
Regulatory Liability, Noncurrent	1,199.4	1,223.5
Other	166.1	170.6
Liabilities, Other than Long-term Debt, Noncurrent, Total	2,486.9	2,485.9
Liabilities, Total	6,389.5	6,118.3
COMMITMENTS AND CONTINGENCIES (NOTE 11)
Stockholders' Equity Attributable to Parent [Abstract]
Common stockholder's equity	1,038.8	1,036.6
Retained earnings	2,895.0	2,921.7
Stockholders' Equity Attributable to Parent, Total	3,933.8	3,958.3
TOTAL LIABILITIES AND STOCKHOLDER'S EQUITY	$ 10,323.3	$ 10,076.6