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Pension and Postretirement Health and Life Benefits (Narrative) (Details) (Defined Benefit Pension Plans [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Defined Benefit Pension Plans [Member]
Expected defined benefit plan contributions for current fiscal year	$ 23.4
Expected defined benefit plan contributions for current fiscal year under ERISA	20.9
Expected defined benefit plan contributions for current fiscal year for non-qualified plans	2.5
USEC contributions	$ 1.3

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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=21915506&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Name:	us-gaap_DefinedBenefitPlanEstimatedFutureEmployerContributionsInCurrentFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

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

+ References

No definition available.

+ Details

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

X

- Definition

Expected defined benefit plan contributions for current fiscal year under ERISA

+ References

No definition available.

+ Details

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