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Pension and Postretirement Health and Life Benefits (Narrative) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2012
Net defined benefit plan costs for former Portsmouth employees	$ 6.6
Defined Benefit Pension Plans [Member]
Expected defined benefit plan contributions for current fiscal year		15.9
Expected defined benefit plan contributions for current fiscal year under ERISA		12.5
Expected defined benefit plan contributions for current fiscal year for non-qualified plans		3.4
Estimated reduction in defined benefit plan contributions for current fiscal year due to MAP-21		10.7
USEC contributions	11.2
Postretirement Health and Life Benefits Plans [Member]
Expected defined benefit plan contributions for current fiscal year		$ 1.4

X

- Definition

The increase in the fair value of plan assets from contributions made by the employer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(3)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

+ Details

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Period Type:	duration

X

- Definition

The employer's best estimate, as soon as it can be reasonably determined, of contributions expected to be paid to the plan in the current remaining fiscal period. Estimated contributions may be presented in the aggregate combining (1) contributions required by funding regulations or laws, (2) discretionary contributions, and (3) noncash contributions.

+ References

No definition available.

+ Details

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X

- Definition

Estimated reduction in defined benefit plan contributions for current fiscal year due to MAP-21

+ References

No definition available.

+ Details

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X

- Definition

Expected defined benefit plan contributions for current fiscal year for non-qualified plans

+ References

No definition available.

+ Details

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X

- Definition

Expected defined benefit plan contributions for current fiscal year under ERISA

+ References

No definition available.

+ Details

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Namespace Prefix:	usu_
Data Type:	xbrli:monetaryItemType
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X

- Definition

Net defined benefit plan costs for former Portsmouth employees

+ References

No definition available.

+ Details

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Namespace Prefix:	usu_
Data Type:	xbrli:monetaryItemType
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