Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Common Stock, Shares Authorized	1,500	1,500
Common stock, shares issued	1	1
Accounts Receivable, Allowance for Credit Loss, Current	$ 8.1	$ 6.1
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
Regulatory assets, non-current	119.5	140.0
Intangible assets, net of amortization	173.8	175.1
Other Assets, Noncurrent	52.3	45.9
Assets, Noncurrent	2,968.4	2,932.4
Liabilities, Current	1,164.5	1,034.2
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
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
Common Stock, Value, Issued	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)
Liabilities	3,124.6	3,055.3
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(589.9)	(571.7)
Property, Plant and Equipment, Net	$ 2,622.8	$ 2,571.4
Subsidiaries [Member]
Common Stock, Shares Authorized	50,000,000	50,000,000
Common Stock, Shares, Outstanding	41,172,173	41,172,173
Common stock, par value (in USD per share)	$ 0.01	$ 0.01
Accounts Receivable, Allowance for Credit Loss, Current	$ 8.1	$ 6.1
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
Regulatory assets, non-current	119.5	140.0
Intangible assets, net of amortization	172.1	173.2
Other Assets, Noncurrent	49.4	43.2
Assets, Noncurrent	2,938.3	2,902.6
Liabilities, Current	733.0	604.3
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
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
Common Stock, Value, Issued	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
Liabilities	2,243.6	2,177.4
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