Operations and Significant Accounting Policies - Supplemental Statement of Cash Flows Information - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2023	Jun. 30, 2022
Supplemental Cash Flow Information [Abstract]
Cash Paid for Interest – Net of Amounts Capitalized		$ 39.1	$ 35.6
Cash Paid for Income Taxes - Net		8.1	1.1
Noncash Investing and Financing Activities [Abstract]
Increase (Decrease) in Accounts Payable for Capital Additions to Property, Plant and Equipment		(5.0)	3.1
Reclassification of Property, Plant and Equipment to Inventory (a)	[1]	0.0	78.6
Capitalized Asset Retirement Costs		2.4	8.8
AFUDC–Equity		1.4	1.7
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents		$ 51.1	$ 81.7

[1] The decommissioning of the legacy Northern Wind assets resulted in a reclassification from Property, Plant and Equipment – Net to Inventories – Net in the second quarter of 2022 as they were repowered and subsequently sold to a subsidiary of Xcel Energy Inc.