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, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Pension Plans [Member]
Obligations at beginning of year	$ 989.5	$ 876.8
Actuarial (gains) losses, net	104.6	93.4
Service costs	14.6	16.2	19.3
Interest costs	48.3	50.3	48.9
Benefits paid	(58.0)	(50.4)
Curtailment losses		3.2	0.4
Obligations at end of year	1,099.0	989.5	876.8
Fair value of plan assets at beginning of year	727.8	728.5
Actual return on plan assets	91.3	34.1
USEC contributions	13.7	15.6
Benefits paid	(58.0)	(50.4)
Fair value of plan assets at end of year	774.8	727.8	728.5
(Unfunded) status at end of year	(324.2)	(261.7)
Amounts recognized in current liabilities	(2.5)	(3.4)
Amounts recognized in noncurrent liabilities	(321.7)	(258.3)
Amounts recognized in assets and liabilities	(324.2)	(261.7)
Amounts recognized in accumulated other comprehensive income, pre-tax, net actuarial loss	326.0	280.5
Amounts recognized in accumulated other comprehensive income, pre-tax, prior service cost (credit)	1.7	3.2
Amounts recognized in accumulated other comprehensive income, pre-tax	327.7	283.7
Discount rate assumption used to determine benefit obligations at end of year	4.07%	4.95%
Compensation increase assumption used to determine benefit obligations at end of year	4.00%	4.25%
Postretirement Health and Life Benefits Plans [Member]
Obligations at beginning of year	252.9	230.6
Actuarial (gains) losses, net	(7.2)	14.7
Service costs	3.7	4.3	5.0
Interest costs	11.1	12.2	11.9
Benefits paid	(12.3)	(11.5)
Less federal subsidy on benefits paid	0.6	0.7
Curtailment losses		1.9
Obligations at end of year	248.8	252.9	230.6
Fair value of plan assets at beginning of year	45.1	51.9
Actual return on plan assets	5.8	(1.8)
USEC contributions	3.0	6.5
Benefits paid	(12.3)	(11.5)
Fair value of plan assets at end of year	41.6	45.1	51.9
(Unfunded) status at end of year	(207.2)	(207.8)
Amounts recognized in noncurrent liabilities	(207.2)	(207.8)
Amounts recognized in assets and liabilities	(207.2)	(207.8)
Amounts recognized in accumulated other comprehensive income, pre-tax, net actuarial loss	45.3	59.9
Amounts recognized in accumulated other comprehensive income, pre-tax	$ 45.3	$ 59.9
Discount rate assumption used to determine benefit obligations at end of year	3.66%	4.46%
Compensation increase assumption used to determine benefit obligations at end of year	4.00%	4.25%

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

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=21915506&loc=d3e1928-114920

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 Pension Cost)

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

Reference 3: 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 4: 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.

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 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 7: 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.