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Pension and Postretirement Health and Life Benefits (Schedule of Fair Value of Plan Assets) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Defined Benefit Pension Plans [Member]
U.S. government securities	$ 70.1
Collective trust - money market funds	21.4
Collective trust - bond funds	41.5
Collective trust - equity funds	362.9
Preferred equity	0.3
Corporate bonds	219.0
Municipal bonds	7.2
Mortgage and asset backed securities	0.8
Fair value of investments by hierarchy level	723.2
Accrued interest receivable	4.2
Unsettled transactions receivable	0.4
Fair value of plan assets at end of year	727.8	728.5	661.7
Defined Benefit Pension Plans [Member] | Level 1 [Member]
Preferred equity	0.3
Fair value of investments by hierarchy level	0.3
Defined Benefit Pension Plans [Member] | Level 2 [Member]
U.S. government securities	70.1
Collective trust - money market funds	21.4
Collective trust - bond funds	41.5
Collective trust - equity funds	362.9
Corporate bonds	218.1
Municipal bonds	7.2
Mortgage and asset backed securities	0.8
Fair value of investments by hierarchy level	722.0
Defined Benefit Pension Plans [Member] | Level 3 [Member]
Corporate bonds	0.9
Fair value of investments by hierarchy level	0.9
Postretirement Health and Life Benefits Plans [Member]
Fair value of plan assets at end of year	$ 45.1	$ 51.9	$ 50.4

X

- Definition

Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Section 35

-Paragraph 50

-URI http://asc.fasb.org/extlink&oid=6867990&loc=d3e12355-114930



Reference 2: 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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 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 Statement of Financial Accounting Standard (FAS)

-Number 87

-Paragraph 49

-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 Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

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

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X

- Definition

Debt (bills, notes or bonds) that are issued by the government of the United States which are short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 8, 9

-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

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

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- Definition

Accrued interest receivable

+ References

No definition available.

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- Definition

Collective trust - bond funds

+ References

No definition available.

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- Definition

Collective trust - equity funds

+ References

No definition available.

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- Definition

Collective trust - money market funds

+ References

No definition available.

+ Details

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- Definition

Corporate bonds

+ References

No definition available.

+ Details

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Balance Type:	debit
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- Definition

Fair value of investments by hierarchy level

+ References

No definition available.

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- Definition

Mortgage and asset backed securities

+ References

No definition available.

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- Definition

Municipal bonds

+ References

No definition available.

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- Definition

Preferred equity

+ References

No definition available.

+ Details

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- Definition

Unsettled transactions receivable

+ References

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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