Common Equity (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Recorded pre-tax share-based compensation expense and related tax benefit for share-based awards made to employees and directors
Share-based compensation expense	$ 13.3	$ 2.1
Related Tax Benefit	5.3	0.8
Common Equity (Textuals) [Abstract]
Minimum percentage award based on performance unit	0.00
Maximum percentage award based on performance unit	1.75
Tax Benefit from Stock Options Exercised	0	3.6
Other Comprehensive Income (Loss), Net of Tax	0
Stock options [Member]
Recorded pre-tax share-based compensation expense and related tax benefit for share-based awards made to employees and directors
Share-based compensation expense	0.7	0.6
Performance units [Member]
Recorded pre-tax share-based compensation expense and related tax benefit for share-based awards made to employees and directors
Share-based compensation expense	11.8	1.0
Common Equity (Textuals) [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	346,570	435,690
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Intrinsic Value	26.7	12.6
Tax Benefit from Stock Options Exercised	9.7	4.3
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	28.6
Employee Service Share-based Compensation, Unrecognized Compensation Costs on Nonvested Awards, Weighted Average Period of Recognition	22
Restricted stock [Member]
Recorded pre-tax share-based compensation expense and related tax benefit for share-based awards made to employees and directors
Share-based compensation expense	0.8	0.5
Common Equity (Textuals) [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	94,959
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Intrinsic Value	2.6	2.1
Tax Benefit from Stock Options Exercised	0	0.6
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 4.8
Employee Service Share-based Compensation, Unrecognized Compensation Costs on Nonvested Awards, Weighted Average Period of Recognition	27

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

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-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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-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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- Definition

As of the balance sheet date, the aggregate unrecognized cost of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

+ References

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-Paragraph A240

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- Definition

The weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, using a decimal to express in number of years.

+ References

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- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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- Definition

This element represents Other Comprehensive Income or Loss, Net of Tax, for the period. Includes deferred gains or losses on qualifying hedges, unrealized holding gains or losses on available-for-sale securities, minimum pension liability, and cumulative translation adjustment. While for technical reasons this element has no balance attribute, the default assumption is a credit balance consistent with its label.

+ References

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 130

-Paragraph 22, 23, 24, 25

-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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-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

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-Publisher FASB

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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-Paragraph 31

-Article 5

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

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-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

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-Paragraph 38

-Subparagraph c(3)

-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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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(2)(c)

-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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- Definition

Reductions in the entity's income taxes that arise when compensation cost (from non-qualified stock options) recognized on the entity's tax return exceeds compensation cost from non-qualified stock options recognized on the income statement. This element increases net cash provided by operating activities.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A132

-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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Maximum percentage award based on performance unit.

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Minimum percentage award based on performance unit.

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period, Total Intrinsic Value

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No definition available.

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