Revenue and Contracts with Customers (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Revenue, nonmonetary transaction				$ 23.4
Nonmonetary transaction, amount of barter transaction		$ 15.0		44.4
Deferred revenue, revenue recognized				5.2
Separative work units owed to others new borrowings			$ 1.7
Separative work units owed to others noncurrent	$ 10.8			10.8
Government cost obligation	74.5			74.5
Loss on contracts					$ 0.0
Provision for Loss on Contracts	8.9			8.9
Accounts receivable, net	14.1			14.1		$ 21.1
Proceeds from settlement with customer				32.4
Revenue, remaining performance obligation, amount	1,000.0			1,000.0
Deferred Revenue and Advances from Customers Approximate	300.0			300.0
Minimum [Member]
Company cost share portion						18.3
Maximum [Member]
Government cost share portion	115.0			115.0
Government [Member]
Provision for Loss on Contracts	8.9			$ 8.9		$ 10.0
Proceeds from Customers	$ 41.5