Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Cash flows from operating activities:
Net income	$ (4.1)	$ 22.5
Adjustments to reconcile net income / (loss) to net cash from operating activities:
Depreciation and amortization	59.6	56.9
Deferred income taxes	(10.7)	2.3
Gain (Loss) on Disposition of Business, Including Discontinued Operation	(0.6)	0.0
Changes in certain assets and liabilities:
Accounts receivable, net	(18.0)	1.5
Inventories	(6.5)	(3.6)
Taxes applicable to subsequent years	62.9	58.6
Deferred regulatory costs, net	55.4	5.1
Prepayments and other current assets	(3.9)	(4.4)
Increase (Decrease) in Other Noncurrent Assets	5.9	(4.8)
Accounts payable	(5.7)	7.1
Accrued taxes payable / receivable	(77.8)	(75.5)
Accrued interest	5.1	2.4
Increase (Decrease) in Other Accrued Liabilities	0.6	(1.6)
Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits	(9.2)	(12.2)
Other	(1.0)	2.2
Net Cash Provided by (Used in) Operating Activities	52.0	56.5
Cash flows from investing activities:
Capital expenditures	(193.0)	(144.5)
Payments for (Proceeds from) Removal Costs	(14.7)	(13.8)
Payments for (Proceeds from) Businesses and Interest in Affiliates	0.0	(1.2)
Other investing activities, net	(0.1)	(0.7)
Net cash used in investing activities	(207.8)	(160.2)
Cash flows from financing activities:
Payments of Deferred Finance Costs	(1.5)	(0.2)
Proceeds from Lines of Credit	185.0	120.0
Repayments of Lines of Credit	(150.0)	0.0
Proceeds from Issuance of Long-term Debt	140.0	0.0
Net cash provided by financing activities	173.5	119.8
Cash, cash equivalents, and restricted cash:
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	17.7	16.1
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	44.4	41.6
Non-cash financing and investing activities:
Accruals for capital expenditures	31.4	15.1
Supplemental cash flow information:
Interest paid, net of amounts capitalized	41.3	41.5
Subsidiaries [Member]
Cash flows from operating activities:
Net income	14.1	40.3
Adjustments to reconcile net income / (loss) to net cash from operating activities:
Depreciation and amortization	58.7	55.8
Deferred income taxes	(6.9)	6.4
Gain (Loss) on Disposition of Business, Including Discontinued Operation	(0.6)	0.0
Changes in certain assets and liabilities:
Accounts receivable, net	(17.7)	1.6
Inventories	(6.5)	(3.6)
Taxes applicable to subsequent years	62.8	58.3
Deferred regulatory costs, net	55.4	5.1
Prepayments and other current assets	(4.5)	(5.2)
Increase (Decrease) in Other Noncurrent Assets	5.7	(5.7)
Accounts payable	(6.8)	6.0
Accrued taxes payable / receivable	(75.9)	(71.0)
Accrued interest	5.3	3.3
Increase (Decrease) in Other Accrued Liabilities	0.2	(1.5)
Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits	(9.2)	(12.2)
Other	(0.8)	3.7
Net Cash Provided by (Used in) Operating Activities	73.3	81.3
Cash flows from investing activities:
Capital expenditures	(191.0)	(143.3)
Payments for (Proceeds from) Removal Costs	(14.5)	(13.8)
Other investing activities, net	0.4	0.9
Net cash used in investing activities	(205.1)	(156.2)
Cash flows from financing activities:
Payments of Dividends	(49.0)	(27.0)
Payments of Deferred Finance Costs	(1.0)	0.0
Proceeds from Lines of Credit	185.0	120.0
Repayments of Lines of Credit	(130.0)	0.0
Proceeds from Issuance of Long-term Debt	140.0	0.0
Net cash provided by financing activities	145.0	93.0
Cash, cash equivalents, and restricted cash:
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	13.2	18.1
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	27.7	29.9
Non-cash financing and investing activities:
Accruals for capital expenditures	31.2	15.1
Supplemental cash flow information:
Interest paid, net of amounts capitalized	$ 12.9	$ 12.6