Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 16.7	$ 25.4
Restricted cash	0.1	0.1
Accounts receivable, net	65.4	69.7
Accounts Receivable, Allowance for Credit Loss, Current	1.7	2.8
Inventories	9.5	8.8
Taxes applicable to subsequent years	38.8	78.0
Regulatory assets, current	34.9	27.5
Income Taxes Receivable, Current	20.3	17.9
Prepayments and other current assets	9.2	5.8
Total current assets	194.9	233.2
Property, plant & equipment:
Property, plant & equipment	1,903.2	1,839.3
Less: Accumulated depreciation and amortization	(442.8)	(415.7)
Property, plant and equipment, net of depreciation	1,460.4	1,423.6
Construction work in process	156.1	141.7
Total net property, plant & equipment	1,616.5	1,565.3
Other non-current assets:
Regulatory assets, non-current	191.6	193.6
Intangible assets, net of amortization	18.9	19.3
Other non-current assets	27.0	24.6
Total other non-current assets	237.5	237.5
Total assets	2,048.9	2,036.0
Current liabilities:
Current portion of long-term debt	180.2	100.2
Accounts payable	73.2	84.5
Accrued taxes	67.0	83.0
Accrued interest	15.6	16.0
Security deposits	18.0	19.4
Regulatory liabilities, current	14.9	18.0
Other current liabilities	17.9	21.0
Total current liabilities	386.8	342.1
Non-current liabilities:
Long-term debt	1,394.2	1,393.4
Deferred taxes	185.9	177.2
Taxes payable	41.4	80.4
Regulatory liabilities, non-current	214.5	218.3
Pension, retiree and other benefits	82.5	93.9
Other deferred credits	12.5	14.2
Total non-current liabilities	1,931.0	1,977.4
Commitments and contingencies
Common shareholder's equity:
Common stock	0.0	0.0
Other paid-in capital	2,468.8	2,468.8
Accumulated other comprehensive income	(11.7)	(12.3)
Retained Earnings (Accumulated Deficit)	(2,726.0)	(2,740.0)
Total common shareholder's equity	(268.9)	(283.5)
Total liabilities and shareholder's equity	$ 2,048.9	$ 2,036.0
Common Stock, Shares Authorized	1,500	1,500
Common stock, shares issued	1	1
Subsidiaries [Member]
Current assets:
Cash and cash equivalents	$ 4.8	$ 11.7
Restricted cash	0.1	0.1
Accounts receivable, net	64.9	70.2
Accounts Receivable, Allowance for Credit Loss, Current	1.7	2.8
Inventories	9.5	8.8
Taxes applicable to subsequent years	38.7	77.6
Regulatory assets, current	34.9	27.5
Income Taxes Receivable, Current	30.7	32.5
Prepayments and other current assets	10.7	6.4
Total current assets	194.3	234.8
Property, plant & equipment:
Property, plant & equipment	2,490.3	2,437.3
Less: Accumulated depreciation and amortization	(1,047.8)	(1,032.1)
Property, plant and equipment, net of depreciation	1,442.5	1,405.2
Construction work in process	152.6	138.8
Total net property, plant & equipment	1,595.1	1,544.0
Other non-current assets:
Regulatory assets, non-current	191.6	193.6
Intangible assets, net of amortization	17.9	18.3
Other non-current assets	26.6	24.0
Total other non-current assets	236.1	235.9
Total assets	2,025.5	2,014.7
Current liabilities:
Current portion of long-term debt	100.2	20.2
Accounts payable	72.3	85.5
Accrued taxes	67.9	82.7
Accrued interest	2.9	2.6
Security deposits	17.8	19.1
Regulatory liabilities, current	14.9	18.0
Other current liabilities	12.5	25.0
Total current liabilities	288.5	253.1
Non-current liabilities:
Long-term debt	573.8	573.9
Deferred taxes	180.4	172.1
Taxes payable	41.3	80.3
Regulatory liabilities, non-current	214.5	218.3
Pension, retiree and other benefits	82.5	93.9
Other deferred credits	6.0	6.4
Total non-current liabilities	1,098.5	1,144.9
Commitments and contingencies
Par value common shares (in USD per share)	$ 0.01	$ 0.01
Common shareholder's equity:
Common stock	$ 0.4
Other paid-in capital	707.4
Accumulated other comprehensive income	(40.2)	$ (42.1)
Retained Earnings (Accumulated Deficit)	(29.1)
Total common shareholder's equity	638.5	616.7
Total liabilities and shareholder's equity	$ 2,025.5	$ 2,014.7
Common Stock, Shares, Outstanding	41,172,173	41,172,173
Common Stock, Shares Authorized	50,000,000	50,000,000