Supplemental Financial Information (Schedule of Components of Other Operating (Income) Expense, Net) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
UTIS fire
Fixed assets write-offs	$ 0.0	$ 0.0	$ 1.1
Inventory charges	0.0	0.2	0.9
Professional services	0.9	1.4	2.7
Lease obligations	0.0	0.4	1.0
Lease impairments	0.0	0.0	0.5
Compensation & benefits	0.0	2.4	2.1
Third-party property claims	0.0	0.0	4.7
Other	0.0	(0.2)	0.1
Insurance recoveries	(31.4)	(6.6)	(6.9)
Total UTIS fire	(30.5)	(2.4)	6.2
Regulatory termination fee, net	0.0	(142.1)	0.0
Loss (gain) on sale or disposal of property, plant and equipment	(2.6)	0.5	(0.9)
Total other operating (income) expense, net	$ (33.1)	$ (144.0)	$ 5.3