Inventories (Schedule of Inventories) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Inventory, Net [Abstract]
Separative work units inventory	$ 7.3	$ 47.2
Uranium inventory	92.7	105.9
Inventories	100.0	153.1
Separative work units owed to customers and suppliers	3.8	15.0
Uranium owed to customers and suppliers	41.3	62.9
Inventories owed to customers and suppliers	45.1	77.9
Separative work units net of liability	3.5	32.2
Uranium inventory net of liability	51.4	43.0
Inventories, net	$ 54.9	$ 75.2

Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.6(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 330
-SubTopic 10
-Section 35
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=68049868&loc=d3e3927-108312

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6676-107765

Name:	us-gaap_InventoryNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant