Pension and Postretirement Health and Life Benefits (Schedule of Changes in Projected Benefit Obligations) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Defined Benefit Pension Plans [Member]
Obligations at beginning of year	$ 876.8	$ 840.0
Actuarial (gains) losses, net	93.4	10.3
Service costs	16.2	19.3	18.7
Interest costs	50.3	48.9	47.7
Benefits paid	(50.4)	(41.7)
Curtailment losses	3.2	0.4
Obligations at end of year	989.5	876.8	840.0
Fair value of plan assets at beginning of year	728.5	661.7
Actual return on plan assets	34.1	95.7
USEC contributions	15.6	12.8
Benefits paid	(50.4)	(41.7)
Fair value of plan assets at end of year	727.8	728.5	661.7
(Unfunded) status at end of year	(261.7)	(148.3)
Amounts recognized in current liabilities	(3.4)	(2.9)
Amounts recognized in noncurrent liabilities	(258.3)	(145.4)
Amounts recognized in assets and liabilities	(261.7)	(148.3)
Amounts recognized in accumulated other comprehensive income, pre-tax, net actuarial loss	280.5	176.7
Amounts recognized in accumulated other comprehensive income, pre-tax, prior service cost (credit)	3.2	4.8
Amounts recognized in accumulated other comprehensive income, pre-tax	283.7	181.5
Postretirement Health and Life Benefits Plans [Member]
Obligations at beginning of year	230.6	219.3
Actuarial (gains) losses, net	14.7	5.0
Service costs	4.3	5.0	4.6
Interest costs	12.2	11.9	12.6
Benefits paid	(11.5)	(10.8)
Less federal subsidy on benefits paid	0.7	0.2
Curtailment losses	1.9
Obligations at end of year	252.9	230.6	219.3
Fair value of plan assets at beginning of year	51.9	50.4
Actual return on plan assets	(1.8)	5.4
USEC contributions	6.5	6.9
Benefits paid	(11.5)	(10.8)
Fair value of plan assets at end of year	45.1	51.9	50.4
(Unfunded) status at end of year	(207.8)	(178.7)
Amounts recognized in noncurrent liabilities	(207.8)	(178.7)
Amounts recognized in assets and liabilities	(207.8)	(178.7)
Amounts recognized in accumulated other comprehensive income, pre-tax, net actuarial loss	59.9	43.6
Amounts recognized in accumulated other comprehensive income, pre-tax, prior service cost (credit)		0.1
Amounts recognized in accumulated other comprehensive income, pre-tax	$ 59.9	$ 43.7

The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Actual Return on Plan Assets (Component of Net Periodic Pension Cost)

-URI http://asc.fasb.org/extlink&oid=6504226

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Actual Return on Plan Assets (Component of Net Periodic Postretirement Benefit Cost)

-URI http://asc.fasb.org/extlink&oid=6504192

Reference 3: 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 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(1)

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

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 106

-Paragraph 518

-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 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 87

-Paragraph 264

-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 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph d(iv)(b)(i)

-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.