Inventories (Schedule of Inventories) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Inventory, Net [Abstract]
Separative work units inventory	$ 10.1	$ 7.8
Uranium inventory	56.5	56.7
Inventories	66.6	64.5
Separative work units owed to customers and suppliers	3.1	0.0
Uranium owed to customers and suppliers	4.7	5.6
Inventories owed to customers and suppliers	7.8	5.6
Separative work units net of liability	7.0	7.8
Uranium inventory net of liability	51.8	51.1
Inventories, net	$ 58.8	$ 58.9