Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities:
Net income	$ 14.0	$ 5.4
Adjustments to reconcile net income to net cash from operating activities:
Deferred income taxes	4.6	33.5
Depreciation and amortization	38.0	36.4
Gain (Loss) on Disposition of Business, Including Discontinued Operation	0.0	(4.5)
Changes in certain assets and liabilities:
Accounts receivable, net	(4.4)	(19.1)
Inventories	0.6	(4.7)
Taxes applicable to subsequent years	(39.2)	(36.8)
Deferred regulatory costs, net	9.8	19.5
Prepayments and other current assets	(5.7)	2.0
Accounts payable	4.1	(10.1)
Accrued taxes payable / receivable	(57.5)	(13.0)
Accrued interest	(0.4)	0.3
Increase (Decrease) in Other Accrued Liabilities	(3.7)	(3.0)
Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits	(11.4)	(9.3)
Other	(1.5)	(4.0)
Net Cash Provided by (Used in) Operating Activities	16.7	82.8
Cash flows from investing activities:
Capital expenditures	(94.9)	(66.9)
Payments for (Proceeds from) Removal Costs	(9.2)	(17.1)
Payments for Removal Costs	(0.8)	(0.6)
Proceeds from Sale of Productive Assets	0.0	5.1
Other investing activities, net	(0.1)	(0.8)
Net cash used in investing activities	(105.0)	(80.3)
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	(0.4)	(6.1)
Repayments of Lines of Credit	0.0	(219.0)
Proceeds from Issuance of Long-term Debt	0.0	415.0
Proceeds from Lines of Credit	80.0	75.0
Net cash provided by financing activities	79.6	362.8
Cash, cash equivalents, and restricted cash:
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect	(8.7)	365.3
Restricted Cash and Cash Equivalents	16.8	412.3
Non-cash financing and investing activities:
Accruals for capital expenditures	15.8	10.1
Non-cash Proceeds from Sale of Business	0.0	3.4
Supplemental cash flow information:
Interest paid, net of amounts capitalized	29.6	41.1
Income Taxes Paid, Net	0.0	(52.0)
Subsidiaries [Member]
Cash flows from operating activities:
Net income	26.9	29.5
Adjustments to reconcile net income to net cash from operating activities:
Deferred income taxes	3.7	1.2
Depreciation and amortization	37.2	35.5
Changes in certain assets and liabilities:
Accounts receivable, net	5.3	4.9
Inventories	(0.6)	1.3
Taxes applicable to subsequent years	38.9	36.8
Deferred regulatory costs, net	(9.8)	(19.5)
Prepayments and other current assets	(6.7)	3.4
Accounts payable	2.6	(8.7)
Accrued taxes payable / receivable	(52.0)	(36.1)
Accrued interest	0.3	(0.1)
Increase (Decrease) in Other Accrued Liabilities	(3.8)	(4.0)
Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits	(11.4)	(9.3)
Other	2.0	3.8
Net Cash Provided by (Used in) Operating Activities	32.6	38.7
Cash flows from investing activities:
Capital expenditures	(94.0)	(63.4)
Payments for (Proceeds from) Removal Costs	(9.2)	(17.1)
Proceeds from Insurance Settlement, Investing Activities	1.0	0.0
Other investing activities, net	(0.1)	(0.7)
Net cash used in investing activities	(102.3)	(81.2)
Cash flows from financing activities:
Payments of Ordinary Dividends, Common Stock	(17.0)	(14.2)
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	(0.2)	(0.3)
Repayments of Lines of Credit	0.0	(115.0)
Proceeds from Lines of Credit	80.0	75.0
Net cash provided by financing activities	62.8	95.4
Cash, cash equivalents, and restricted cash:
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect	(6.9)	52.9
Restricted Cash and Cash Equivalents	4.9	74.2
Non-cash financing and investing activities:
Accruals for capital expenditures	15.7	10.0
Supplemental cash flow information:
Interest paid, net of amounts capitalized	$ 10.2	$ 10.2