Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
CURRENT ASSETS:
Cash and cash equivalents	$ 81.2	$ 54.0
Accounts Receivable, after Allowance for Credit Loss, Current	131.4	106.8
Inventories	72.1	70.5
Taxes applicable to subsequent years	101.8	137.1
Regulatory assets, current	93.7	82.0
Income Taxes Receivable, Current	29.4	27.1
Prepayments and other current assets	11.4	7.5
Total current assets	521.0	485.0
Property, Plant and Equipment, Net [Abstract]
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(589.9)	(571.7)
Property, Plant and Equipment, Net	2,622.8	2,571.4
Other Assets, Noncurrent [Abstract]
Regulatory assets, non-current	119.5	140.0
Intangible assets, net of amortization	173.8	175.1
Other non-current assets	52.3	45.9
Assets, Noncurrent	2,968.4	2,932.4
Total assets	3,489.4	3,417.4
Current liabilities:
Current portion of long-term debt	784.8	704.4
Accounts payable	154.9	132.1
Accrued taxes	129.9	115.4
Accrued interest	25.8	22.8
Contract with Customer, Liability, Current	20.4	14.2
Regulatory liabilities, current	7.8	10.3
Other current liabilities	40.9	35.0
Total current liabilities	1,164.5	1,034.2
Non-current liabilities:
Long-term debt	1,425.9	1,425.6
Deferred Tax Liabilities, Net	254.3	249.6
Taxes payable	68.3	137.5
Regulatory liabilities, non-current	173.2	169.4
Pension, retiree and other benefits	30.9	30.7
Other deferred credits	7.5	8.3
Total non-current liabilities	1,960.1	2,021.1
Commitments and contingencies
Common shareholder's equity:
Common stock	0.0	0.0
Other paid-in capital	3,040.5	3,040.5
Accumulated other comprehensive income	(5.3)	(5.3)
Retained Earnings (Accumulated Deficit)	(2,670.4)	(2,673.1)
Total common shareholder's equity	364.8	362.1
Total liabilities and shareholder's equity	$ 3,489.4	$ 3,417.4
Common Stock, Shares Authorized	1,500	1,500
Common stock, shares issued	1	1
Liabilities	$ 3,124.6	$ 3,055.3
Subsidiaries [Member]
CURRENT ASSETS:
Cash and cash equivalents	60.4	24.6
Accounts Receivable, after Allowance for Credit Loss, Current	131.2	106.6
Inventories	70.7	69.0
Taxes applicable to subsequent years	101.8	137.1
Regulatory assets, current	93.7	82.0
Income Taxes Receivable, Current	24.9	24.9
Prepayments and other current assets	11.6	8.4
Total current assets	494.3	452.6
Property, Plant and Equipment, Net [Abstract]
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(1,127.9)	(1,115.5)
Property, Plant and Equipment, Net	2,597.3	2,546.2
Other Assets, Noncurrent [Abstract]
Regulatory assets, non-current	119.5	140.0
Intangible assets, net of amortization	172.1	173.2
Other non-current assets	49.4	43.2
Assets, Noncurrent	2,938.3	2,902.6
Total assets	3,432.6	3,355.2
Current liabilities:
Current portion of long-term debt	370.1	290.1
Accounts payable	154.2	132.1
Accrued taxes	130.4	115.2
Accrued interest	13.4	10.2
Contract with Customer, Liability, Current	20.4	14.2
Regulatory liabilities, current	7.8	10.3
Other current liabilities	36.7	32.2
Total current liabilities	733.0	604.3
Non-current liabilities:
Long-term debt	1,012.8	1,012.7
Deferred Tax Liabilities, Net	220.8	217.6
Taxes payable	68.3	137.5
Regulatory liabilities, non-current	173.2	169.4
Pension, retiree and other benefits	30.9	30.7
Other deferred credits	4.6	5.2
Total non-current liabilities	1,510.6	1,573.1
Commitments and contingencies
Par value common shares (in USD per share)	$ 0.01	$ 0.01
Common shareholder's equity:
Common stock	$ 0.4	$ 0.4
Other paid-in capital	1,177.6	1,177.6
Accumulated other comprehensive income	(25.9)	(26.4)
Retained Earnings (Accumulated Deficit)	36.9	26.2
Total common shareholder's equity	1,189.0	1,177.8
Total liabilities and shareholder's equity	$ 3,432.6	$ 3,355.2
Common Stock, Shares, Outstanding	41,172,173	41,172,173
Common Stock, Shares Authorized	50,000,000	50,000,000
Liabilities	$ 2,243.6	$ 2,177.4