Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
CURRENT ASSETS:
Cash and cash equivalents	$ 24.2	$ 41.0
Accounts Receivable, after Allowance for Credit Loss, Current	99.8	92.5
Inventories	52.0	44.5
Taxes applicable to subsequent years	83.4	113.0
Regulatory assets, current	63.9	56.6
Income Taxes Receivable, Current	13.0	8.9
Prepayments and other current assets	7.4	6.6
Total current assets	343.7	363.1
Property, plant & equipment:
Property, plant & equipment	2,562.4	2,521.9
Less: Accumulated depreciation and amortization	(548.7)	(535.1)
Property, plant and equipment, net of depreciation	2,013.7	1,986.8
Construction work in process	298.7	234.2
Total net property, plant & equipment	2,312.4	2,221.0
Other non-current assets:
Regulatory assets, non-current	146.0	155.7
Intangible assets, net of amortization	130.9	114.0
Other non-current assets	54.7	52.4
Total other non-current assets	331.6	322.1
Total assets	2,987.7	2,906.2
Current liabilities:
Current portion of long-term debt	170.2	15.2
Accounts payable	124.3	163.9
Accrued taxes	109.9	101.6
Accrued interest	25.8	16.9
Contract with Customer, Liability, Current	20.4	12.7
Regulatory liabilities, current	16.8	18.0
Other current liabilities	21.8	22.6
Total current liabilities	489.2	350.9
Non-current liabilities:
Long-term debt	1,838.0	1,837.4
Deferred Tax Liabilities, Net	233.3	227.3
Taxes payable	56.0	113.4
Regulatory liabilities, non-current	180.6	182.1
Pension, retiree and other benefits	30.7	37.7
Other deferred credits	8.6	8.5
Total non-current liabilities	2,347.2	2,406.4
Commitments and contingencies
Common shareholder's equity:
Common stock	0.0	0.0
Other paid-in capital	2,840.4	2,840.4
Accumulated other comprehensive income	(4.8)	(4.6)
Retained Earnings (Accumulated Deficit)	(2,684.3)	(2,686.9)
Total common shareholder's equity	151.3	148.9
Total liabilities and shareholder's equity	$ 2,987.7	$ 2,906.2
Common Stock, Shares Authorized	1,500	1,500
Common stock, shares issued	1	1
Subsidiaries [Member]
CURRENT ASSETS:
Cash and cash equivalents	$ 7.6	$ 15.5
Accounts Receivable, after Allowance for Credit Loss, Current	100.7	93.1
Inventories	51.4	44.5
Taxes applicable to subsequent years	83.4	112.9
Regulatory assets, current	63.9	56.6
Income Taxes Receivable, Current	24.4	24.4
Prepayments and other current assets	7.5	8.1
Total current assets	338.9	355.1
Property, plant & equipment:
Property, plant & equipment	3,099.7	3,063.2
Less: Accumulated depreciation and amortization	(1,107.8)	(1,098.1)
Property, plant and equipment, net of depreciation	1,991.9	1,965.1
Construction work in process	295.4	230.8
Total net property, plant & equipment	2,287.3	2,195.9
Other non-current assets:
Regulatory assets, non-current	146.0	155.7
Intangible assets, net of amortization	128.7	111.4
Other non-current assets	55.0	52.9
Total other non-current assets	329.7	320.0
Total assets	2,955.9	2,871.0
Current liabilities:
Current portion of long-term debt	170.2	15.2
Accounts payable	123.3	163.8
Accrued taxes	109.8	101.4
Accrued interest	13.4	4.2
Contract with Customer, Liability, Current	20.4	12.7
Regulatory liabilities, current	16.8	18.0
Other current liabilities	19.4	20.2
Total current liabilities	473.3	335.5
Non-current liabilities:
Long-term debt	1,012.4	1,012.3
Deferred Tax Liabilities, Net	209.0	206.1
Taxes payable	56.0	113.4
Regulatory liabilities, non-current	180.6	182.1
Pension, retiree and other benefits	30.7	37.7
Other deferred credits	4.8	4.7
Total non-current liabilities	1,493.5	1,556.3
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	977.5	977.4
Accumulated other comprehensive income	(27.5)	(27.9)
Retained Earnings (Accumulated Deficit)	38.7	29.3
Total common shareholder's equity	989.1	979.2
Total liabilities and shareholder's equity	$ 2,955.9	$ 2,871.0
Common Stock, Shares, Outstanding	41,172,173	41,172,173
Common Stock, Shares Authorized	50,000,000	50,000,000