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Property, Plant and Equipment Property, Plant and Equipment (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2013 | Jun. 30, 2013
Property, Plant and Equipment [Abstract] |  |
Asset Retirement Charges | $ 19.3 | $ 19.3

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

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- Definition Asset Retirement Charges + References No definition available. + Details
Name: | usu_AssetRetirementCharges
Namespace Prefix: | usu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration