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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, 2014
Defined Benefit Pension Plans [Member]
Expected defined benefit plan contributions for current fiscal year	$ 28.7
Expected defined benefit plan contributions for current fiscal year under ERISA	26.5
Expected defined benefit plan contributions for current fiscal year for non-qualified plans	2.2
USEC contributions	5.8
Defined Benefit Plan, Lump Sum Benefits Paid	$ 5.0

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 Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(3)

-URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920

+ Details

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

X

- Definition

Amount of employer's best estimate of contributions expected to be paid to the plan in the current remaining fiscal period.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Defined Benefit Plan, Lump Sum Benefits Paid

+ References

No definition available.

+ Details

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

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