Operations and Significant Accounting Policies - Other Income (Expense) - Other (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other		$ 22.4	$ 8.7	$ 14.7
Pension and Other Postretirement Benefit Plans Non-Service Credit [Member]
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other	[1]	9.8	6.1	8.6
Interest and Investment Earnings [Member]
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other		0.0	2.3	1.6
AFUDC - Equity [Member]
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other		2.7	2.6	1.9
Gain on Land Sales [Member]
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other		0.0	0.1	0.4
PSA Liability
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other	[2]	10.2	0.0	0.0
Other Income (Expense) - Other [Member]
Other Income (Expense) - Other [Line Items]
Total Other Income (Expense) - Other		$ (0.3)	$ (2.4)	$ 2.2

[1] These are components of net periodic pension and other postretirement benefit cost other than service cost. (See Note 12. Pension and Other Postretirement Benefit Plans.)

[2] The gain on removal of the PSA liability for the Northern Wind project upon decommissioning of the legacy wind energy facility assets, which was more than offset by a reserve for an anticipated loss on the sale of the Northern Wind project, was recorded in Cost of Sales - Non-Utility on the Consolidated Statement of Income.