Operations and Significant Accounting Policies - Supplemental Statement of Cash Flows Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash Paid During the Period for Interest – Net of Amounts Capitalized	$ 80.5	$ 72.8	$ 66.8
Cash Paid for Income Taxes	19.5	6.0	0.0
Noncash Investing and Financing Activities
Increase (Decrease) in Accounts Payable for Capital Additions to Property, Plant and Equipment	2.2	(9.6)	(14.0)
Reclassification of Property, Plant and Equipment to Inventory	0.0	99.7	0.0
Reclassification of Redeemable Non-Controlling Interest to Current Liabilities	0.0	0.0	30.6
Capitalized Asset Retirement Costs	5.8	11.8	16.9
AFUDC–Equity	$ 3.6	$ 2.7	$ 2.6