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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, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Pension Plans [Member]
U.S. government securities	$ 89.8	$ 70.1
Collective trust - money market funds	16.5	21.4
Collective trust - bond funds	47.7	41.5
Collective trust - equity funds	397.4	362.9
Preferred equity		0.3
Corporate bonds	211.7	219.0
Municipal bonds	7.8	7.2
Mortgage and asset backed securities	0.2	0.8
Fair value of investments by hierarchy level	771.1	723.2
Accrued interest receivable	3.8	4.2
Unsettled transactions receivable	(0.1)	0.4
Fair value of plan assets at end of year	774.8	727.8	728.5
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	89.8	70.1
Collective trust - money market funds	16.5	21.4
Collective trust - bond funds	47.7	41.5
Collective trust - equity funds	397.4	362.9
Corporate bonds	211.1	218.1
Municipal bonds	7.8	7.2
Mortgage and asset backed securities	0.2	0.8
Fair value of investments by hierarchy level	770.5	722.0
Defined Benefit Pension Plans [Member] | Level 3 [Member]
Corporate bonds	0.6	0.9
Fair value of investments by hierarchy level	0.6	0.9
Postretirement Health and Life Benefits Plans [Member]
Money market funds	0.8	1.2
Bond mutual funds	13.7	14.4
Equity mutual funds	27.1	29.5
Fair value of plan assets at end of year	41.6	45.1	51.9
Postretirement Health and Life Benefits Plans [Member] | Level 1 [Member]
Money market funds	0.8	1.2
Bond mutual funds	13.7	14.4
Equity mutual funds	27.1	29.5
Fair value of plan assets at end of year	$ 41.6	$ 45.1

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 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 3: 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 4: 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 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=21915506&loc=d3e1928-114920

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- 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 Accounting Standards Codification

-Glossary Cash Equivalents

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



Reference 2: 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.

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Accrued interest receivable

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- Definition

Bond mutual funds

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- Definition

Collective trust - bond funds

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- Definition

Collective trust - equity funds

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Collective trust - money market funds

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- Definition

Corporate bonds

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Equity mutual funds

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Fair value of investments by hierarchy level

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- Definition

Money market funds

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- Definition

Mortgage and asset backed securities

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Municipal bonds

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Preferred equity

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Unsettled transactions receivable

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