Inventories (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Inventory, Net [Abstract]
Separative work units inventory	$ 827.6	$ 880.9
Uranium inventory	345.0	703.7
Materials and supplies	4.2	8.6
Inventories	1,176.8	1,593.2
Separative work units owed to customers and suppliers	225.7	382.7
Uranium owed to customers and suppliers	250.2	567.3
Inventories owed to customers and suppliers	475.9	950.0
Separative work units net of liability	601.9	498.2
Uranium inventory net of liability	94.8	136.4
Inventories, net	$ 700.9	$ 643.2