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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

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- Details

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- Definition

Asset Retirement Charges

+ References

No definition available.

+ Details

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