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Segment Information (Segment Assets) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenue by Geographic Area, Major Customers and Segment Information
LEU segment assets	$ 2,208.5	$ 3,491.4	$ 3,760.6
Contract services segment assets	$ 57.9	$ 57.9	$ 87.6

X

- Details

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- Definition

Contract services segment assets

+ References

No definition available.

+ Details

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Namespace Prefix:	usu_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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- Definition

LEU segment assets

+ References

No definition available.

+ Details

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Namespace Prefix:	usu_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant