CONDENSED BALANCE SHEETS (Unaudited) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
CURRENT ASSETS
Accounts receivable, less reserve of $1.1 and $1.5, respectively	$ 140.7	$ 153.8
Accrued unbilled revenues	58.9	64.7
Advances to parent	265.8	304.8
Fuel inventories	45.5	46.3
Materials and supplies, at average cost	97.2	90.6
Fuel clause under recoveries	0.0	39.5
Other	24.1	19.6
Total current assets	632.2	719.3
OTHER PROPERTY AND INVESTMENTS	4.6	4.7
PROPERTY, PLANT AND EQUIPMENT
In service	12,856.4	12,765.0
Construction work in progress	149.5	141.6
Total property, plant and equipment	13,005.9	12,906.6
Less: accumulated depreciation	3,920.9	3,868.1
Net property, plant and equipment	9,085.0	9,038.5
DEFERRED CHARGES AND OTHER ASSETS
Regulatory assets	300.0	306.0
Other	8.9	8.1
Total deferred charges and other assets	308.9	314.1
TOTAL ASSETS	10,030.7	10,076.6
Liabilities, Current [Abstract]
Accounts payable	143.1	175.0
Customer deposits	83.2	83.0
Accrued taxes	24.8	41.9
Accrued interest	35.8	37.9
Accrued compensation	19.7	29.5
Fuel clause over recoveries	15.6	4.8
Other	48.4	65.1
Total current liabilities	370.6	437.2
Long-term Debt, Excluding Current Maturities	3,195.6	3,195.2
Liabilities, Other than Long-term Debt, Noncurrent [Abstract]
Accrued benefit obligations	129.7	133.3
Deferred income taxes	961.0	951.4
Deferred investment tax credits	7.1	7.1
Regulatory Liability, Noncurrent	1,216.1	1,223.5
Other	171.5	170.6
Liabilities, Other than Long-term Debt, Noncurrent, Total	2,485.4	2,485.9
Liabilities, Total	6,051.6	6,118.3
COMMITMENTS AND CONTINGENCIES (NOTE 11)
Stockholders' Equity Attributable to Parent [Abstract]
Common stockholder's equity	1,037.5	1,036.6
Retained earnings	2,941.6	2,921.7
Stockholders' Equity Attributable to Parent, Total	3,979.1	3,958.3
TOTAL LIABILITIES AND STOCKHOLDER'S EQUITY	$ 10,030.7	$ 10,076.6