Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash flows from operating activities:
Net income	$ 15.4	$ 13.6
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	19.5	19.1
Deferred income taxes	(0.4)	3.5
Gain (Loss) on Disposition of Business, Including Discontinued Operation	(0.6)	0.0
Changes in certain assets and liabilities:
Accounts receivable, net	(2.3)	6.0
Inventories	(3.0)	(0.3)
Taxes applicable to subsequent years	22.3	20.0
Deferred regulatory costs, net	10.4	(4.8)
Accounts payable	(15.7)	(1.6)
Accrued taxes payable / receivable	(43.3)	(40.2)
Accrued interest	3.0	2.4
Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits	(8.0)	(10.5)
Other	2.5	(1.7)
Net Cash Provided by (Used in) Operating Activities	(0.2)	5.5
Cash flows from investing activities:
Capital expenditures	(64.4)	(51.9)
Payments for (Proceeds from) Removal Costs	(5.0)	(4.5)
Other investing activities, net	0.1	(0.4)
Net cash used in investing activities	(69.3)	(56.8)
Cash flows from financing activities:
Proceeds from Lines of Credit	95.0	60.0
Repayments of Lines of Credit	(20.0)	0.0
Net cash provided by financing activities	75.0	60.0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	5.5	8.7
Cash, cash equivalents, and restricted cash:
Restricted Cash and Cash Equivalents	32.2	34.2
Non-cash financing and investing activities:
Accruals for capital expenditures	23.7	16.3
Supplemental cash flow information:
Interest paid, net of amounts capitalized	11.3	12.9
Subsidiaries [Member]
Cash flows from operating activities:
Net income	16.9	18.3
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	19.2	18.7
Deferred income taxes	2.0	3.2
Gain (Loss) on Disposition of Business, Including Discontinued Operation	(0.6)	0.0
Changes in certain assets and liabilities:
Accounts receivable, net	(1.7)	5.9
Inventories	(3.0)	(0.3)
Taxes applicable to subsequent years	22.3	19.7
Deferred regulatory costs, net	10.4	(4.8)
Accounts payable	(16.7)	(4.3)
Accrued taxes payable / receivable	(38.8)	(38.8)
Accrued interest	3.3	3.2
Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits	(8.0)	(10.5)
Other	0.9	1.0
Net Cash Provided by (Used in) Operating Activities	6.2	11.3
Cash flows from investing activities:
Capital expenditures	(64.2)	(51.6)
Payments for (Proceeds from) Removal Costs	(5.0)	(4.5)
Other investing activities, net	0.5	(0.1)
Net cash used in investing activities	(68.7)	(56.2)
Cash flows from financing activities:
Payments of Ordinary Dividends, Common Stock	(9.0)	(10.0)
Proceeds from Lines of Credit	95.0	60.0
Repayments of Lines of Credit	(20.0)	0.0
Net cash provided by financing activities	66.0	50.0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	3.5	5.1
Cash, cash equivalents, and restricted cash:
Restricted Cash and Cash Equivalents	18.0	16.9
Non-cash financing and investing activities:
Accruals for capital expenditures	23.6	16.0
Supplemental cash flow information:
Interest paid, net of amounts capitalized	$ 1.8	$ 2.7