Operations and Significant Accounting Policies - Supplemental Statement of Cash Flows Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash Paid for Interest – Net of Amounts Capitalized	$ 64.8	$ 60.5
Cash Paid for Income Taxes – Net	14.1	1.1
Noncash Investing and Financing Activities
Increase in Accounts Payable for Capital Additions to Property, Plant and Equipment	11.8	2.4
Reclassification of Property, Plant and Equipment to Inventory	0.0	99.8
Capitalized Asset Retirement Costs	2.4	9.0
AFUDC–Equity	$ 2.5	$ 2.4