Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net income	$ 22.5	$ (2.8)
Adjustments to reconcile net income / (loss) to net cash from operating activities:
Deferred income taxes	2.3	32.3
Depreciation and amortization	56.9	55.1
Gain (Loss) on Disposition of Business, Including Discontinued Operation	0.0	(4.5)
Changes in certain assets and liabilities:
Accounts receivable, net	1.5	12.7
Inventories	(3.6)	5.5
Taxes applicable to subsequent years	58.6	57.8
Deferred regulatory costs, net	5.1	(17.1)
Prepayments and other current assets	(4.4)	2.5
Increase (Decrease) in Other Noncurrent Assets	(4.8)	2.7
Accounts payable	7.1	(24.6)
Accrued taxes payable / receivable	(75.5)	(63.0)
Accrued interest	2.4	7.4
Increase (Decrease) in Other Accrued Liabilities	(1.6)	(4.5)
Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits	(12.2)	(10.8)
Other	2.2	1.3
Net Cash Provided by (Used in) Operating Activities	56.5	81.7
Cash flows from investing activities:
Capital expenditures	(144.5)	(107.5)
Payments for (Proceeds from) Removal Costs	(13.8)	(21.2)
Payments for Removal Costs	(1.2)	(1.0)
Proceeds from Sale of Productive Assets	0.0	5.1
Other investing activities, net	(0.7)	(0.8)
Net cash used in investing activities	(160.2)	(125.4)
Cash flows from financing activities:
Proceeds from (Payments for) Other Financing Activities	0.0	(0.1)
Proceeds from Contributions from Parent	0.0	98.0
Payments of Deferred Finance Costs	(0.2)	(7.8)
Repayments of Lines of Credit	0.0	(219.0)
Proceeds from Issuance of Long-term Debt	0.0	555.0
Retirement of long-term debt	0.0	(550.8)
Proceeds from Lines of Credit	120.0	165.0
Net cash provided by financing activities	119.8	40.3
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	16.1	(3.4)
Cash, cash equivalents, and restricted cash:
Restricted Cash and Cash Equivalents	41.6	43.6
Non-cash financing and investing activities:
Accruals for capital expenditures	15.1	16.5
Non-cash Proceeds from Sale of Business	0.0	3.0
Supplemental cash flow information:
Interest paid, net of amounts capitalized	41.5	49.7
Income Taxes Paid, Net	0.0	(51.9)
Gain (Loss) on Extinguishment of Debt	0.0	31.7
Subsidiaries [Member]
Cash flows from operating activities:
Net income	40.3	47.3
Adjustments to reconcile net income / (loss) to net cash from operating activities:
Deferred income taxes	6.4	(0.1)
Depreciation and amortization	55.8	53.7
Changes in certain assets and liabilities:
Accounts receivable, net	1.6	1.7
Inventories	(3.6)	2.1
Taxes applicable to subsequent years	58.3	57.7
Deferred regulatory costs, net	5.1	(17.1)
Prepayments and other current assets	(5.2)	4.1
Increase (Decrease) in Other Noncurrent Assets	(5.7)	1.0
Accounts payable	6.0	(20.6)
Accrued taxes payable / receivable	(71.0)	(71.6)
Accrued interest	3.3	4.6
Increase (Decrease) in Other Accrued Liabilities	(1.5)	(4.8)
Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits	(12.2)	(10.8)
Other	3.7	2.5
Net Cash Provided by (Used in) Operating Activities	81.3	49.7
Cash flows from investing activities:
Capital expenditures	(143.3)	(103.9)
Payments for (Proceeds from) Removal Costs	(13.8)	(21.2)
Other investing activities, net	0.9	(0.7)
Net cash used in investing activities	(156.2)	(125.8)
Cash flows from financing activities:
Payments of Ordinary Dividends, Common Stock	(27.0)	(27.7)
Proceeds from (Payments for) Other Financing Activities	0.0	(0.1)
Proceeds from Contributions from Parent	0.0	150.0
Payments of Deferred Finance Costs	0.0	(1.2)
Repayments of Lines of Credit	0.0	(115.0)
Proceeds from Issuance of Long-term Debt	0.0	140.0
Retirement of long-term debt	0.0	(140.0)
Proceeds from Lines of Credit	120.0	75.0
Net cash provided by financing activities	93.0	81.0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	18.1	4.9
Cash, cash equivalents, and restricted cash:
Restricted Cash and Cash Equivalents	29.9	26.2
Non-cash financing and investing activities:
Accruals for capital expenditures	15.1	16.4
Supplemental cash flow information:
Interest paid, net of amounts capitalized	12.6	10.5
Proceeds from Income Tax Refunds	$ 0.0	$ 0.1