Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Common Stock, Shares Authorized	1,500	1,500
Common stock, shares issued	1	1
Accounts Receivable, Allowance for Credit Loss, Current	$ 1.8	$ 0.9
Cash and cash equivalents	41.0	41.0
Accounts Receivable, after Allowance for Credit Loss, Current	101.4	92.5
Inventories	72.3	44.5
Taxes applicable to subsequent years	26.3	113.0
Regulatory assets, current	71.4	56.6
Income Taxes Receivable, Current	25.5	8.9
Prepayments and other current assets	14.3	6.6
Property, plant & equipment	2,799.8	2,521.9
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(577.2)	(535.1)
Construction work in process	269.5	234.2
Regulatory assets, non-current	146.2	155.7
Intangible assets, net of amortization	162.4	114.0
Other Assets, Noncurrent	47.6	52.4
Liabilities, Current	945.3	350.9
Current portion of long-term debt	609.0	15.2
Accounts payable	123.5	163.9
Accrued taxes	114.6	101.6
Accrued interest	25.1	16.9
Contract with Customer, Liability, Current	22.1	12.7
Regulatory liabilities, current	15.8	18.0
Other current liabilities	35.2	22.6
Long-term debt	1,425.3	1,837.4
Deferred Tax Liabilities, Net	245.3	227.3
Taxes payable	0.4	113.4
Regulatory liabilities, non-current	172.2	182.1
Pension, retiree and other benefits	31.6	37.7
Other deferred credits	8.8	8.5
Common Stock, Value, Issued	0.0	0.0
Other paid-in capital	3,040.5	2,840.4
Accumulated other comprehensive income	(5.1)	(4.6)
Retained Earnings (Accumulated Deficit)	(2,663.8)	(2,686.9)
Liabilities	$ 2,828.9	$ 2,757.3
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	$ 1.8	$ 0.9
Cash and cash equivalents	19.6	15.5
Accounts Receivable, after Allowance for Credit Loss, Current	101.1	93.1
Inventories	70.9	44.5
Taxes applicable to subsequent years	26.3	112.9
Regulatory assets, current	71.4	56.6
Income Taxes Receivable, Current	24.8	24.4
Prepayments and other current assets	16.1	8.1
Property, plant & equipment	3,324.3	3,063.2
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(1,125.8)	(1,098.1)
Construction work in process	268.4	230.8
Regulatory assets, non-current	146.2	155.7
Intangible assets, net of amortization	160.4	111.4
Other Assets, Noncurrent	46.5	52.9
Liabilities, Current	514.7	335.5
Current portion of long-term debt	195.0	15.2
Accounts payable	122.4	163.8
Accrued taxes	114.5	101.4
Accrued interest	12.7	4.2
Contract with Customer, Liability, Current	22.1	12.7
Regulatory liabilities, current	15.8	18.0
Other current liabilities	32.2	20.2
Long-term debt	1,012.6	1,012.3
Deferred Tax Liabilities, Net	217.2	206.1
Taxes payable	0.4	113.4
Regulatory liabilities, non-current	172.2	182.1
Pension, retiree and other benefits	31.6	37.7
Other deferred credits	5.0	4.7
Common Stock, Value, Issued	0.4	0.4
Other paid-in capital	1,177.5	977.4
Accumulated other comprehensive income	(26.7)	(27.9)
Retained Earnings (Accumulated Deficit)	45.3	29.3
Liabilities	$ 1,953.7	$ 1,891.8