Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 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	$ 1.0	$ 0.9
Cash and cash equivalents	48.4	41.0
Accounts Receivable, after Allowance for Credit Loss, Current	94.4	92.5
Inventories	57.6	44.5
Taxes applicable to subsequent years	53.0	113.0
Regulatory assets, current	76.5	56.6
Income Taxes Receivable, Current	18.0	8.9
Prepayments and other current assets	9.4	6.6
Property, plant & equipment	2,647.8	2,521.9
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(563.9)	(535.1)
Construction work in process	355.6	234.2
Regulatory assets, non-current	144.1	155.7
Intangible assets, net of amortization	140.9	114.0
Other Assets, Noncurrent	51.9	52.4
Liabilities, Current	492.4	350.9
Current portion of long-term debt	135.2	15.2
Accounts payable	167.8	163.9
Accrued taxes	106.9	101.6
Accrued interest	22.9	16.9
Contract with Customer, Liability, Current	13.5	12.7
Regulatory liabilities, current	17.2	18.0
Other current liabilities	28.9	22.6
Long-term debt	1,838.6	1,837.4
Deferred Tax Liabilities, Net	240.2	227.3
Taxes payable	53.4	113.4
Regulatory liabilities, non-current	177.7	182.1
Pension, retiree and other benefits	31.1	37.7
Other deferred credits	9.0	8.5
Common Stock, Value, Issued	0.0	0.0
Other paid-in capital	2,970.4	2,840.4
Accumulated other comprehensive income	(5.0)	(4.6)
Retained Earnings (Accumulated Deficit)	(2,674.1)	(2,686.9)
Liabilities	$ 2,842.4	$ 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	$ 1.0	$ 0.9
Cash and cash equivalents	22.2	15.5
Accounts Receivable, after Allowance for Credit Loss, Current	93.7	93.1
Inventories	56.6	44.5
Taxes applicable to subsequent years	53.0	112.9
Regulatory assets, current	76.5	56.6
Income Taxes Receivable, Current	24.4	24.4
Prepayments and other current assets	9.4	8.1
Property, plant & equipment	3,177.7	3,063.2
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(1,118.2)	(1,098.1)
Construction work in process	354.5	230.8
Regulatory assets, non-current	144.1	155.7
Intangible assets, net of amortization	138.8	111.4
Other Assets, Noncurrent	51.6	52.9
Liabilities, Current	477.3	335.5
Current portion of long-term debt	135.2	15.2
Accounts payable	167.9	163.8
Accrued taxes	107.4	101.4
Accrued interest	10.2	4.2
Contract with Customer, Liability, Current	13.5	12.7
Regulatory liabilities, current	17.2	18.0
Other current liabilities	25.9	20.2
Long-term debt	1,012.5	1,012.3
Deferred Tax Liabilities, Net	213.5	206.1
Taxes payable	53.4	113.4
Regulatory liabilities, non-current	177.7	182.1
Pension, retiree and other benefits	31.1	37.7
Other deferred credits	5.2	4.7
Common Stock, Value, Issued	0.4	0.4
Other paid-in capital	1,107.5	977.4
Accumulated other comprehensive income	(27.1)	(27.9)
Retained Earnings (Accumulated Deficit)	32.8	29.3
Liabilities	$ 1,970.7	$ 1,891.8