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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
Name: | us-gaap_SegmentReportingInformationRevenueAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Contract services segment assets + References No definition available. + Details
Name: | usu_ContractServicesSegmentAssets
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
Name: | usu_LeuSegmentAssets
Namespace Prefix: | usu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant