Operations and Significant Accounting Policies - Other Income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Other Income (Expense) - Other [Line Items]
Total Other Income		$ 2.0	$ 3.3
Pension and Other Postretirement Benefit Plans Non-Service Credit [Member]
Other Income (Expense) - Other [Line Items]
Total Other Income	[1]	2.6	1.9
Interest and Investment Income (Loss) [Member]
Other Income (Expense) - Other [Line Items]
Total Other Income		0.1	1.1
AFUDC - Equity [Member]
Other Income (Expense) - Other [Line Items]
Total Other Income		0.9	0.5
Other [Member]
Other Income (Expense) - Other [Line Items]
Total Other Income		$ (1.6)	$ (0.2)

[1] These are components of net periodic pension and other postretirement benefit cost other than service cost. (See Note 9. Pension and Other Postretirement Benefit Plans.)