Stock-Based Compensation (Details 3) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2011 M	Dec. 31, 2010	Dec. 31, 2009
Stock Based Compensation
Minimum vesting period (in years)	P1Y
Restricted Stock Awards
Stock Based Compensation
Minimum vesting period (in years)	P1Y
Maximum vesting period (in years)	P5Y
Compensation expense (benefit) related to stock-based awards	$ 12.7	$ 9.5	$ 16.7
Tax benefits received with restricted stock awards (in dollars)	9.4	10.0	6.7
Summarized share information for restricted stock awards
Outstanding, beginning of year (in shares)	1,080	1,017	1,033
Granted (in shares)	622	832	866
Released to participants (in shares)	(686)	(713)	(701)
Canceled (in shares)	(48)	(56)	(181)
Outstanding, end of year (in shares)	968	1,080	1,017
Weighted-average fair value of restricted stock granted (in dollars per share)	$ 30.27	$ 34.83	$ 19.83
Total fair value of shares for which restriction has lapsed (in dollars)	23.3	24.9	16.5
Unrecognized compensation cost related to the unvested portion of outstanding stock-based awards (in dollars)	9.2
Period over which unrecognized compensation is expected to be recognized (in months)	31
Unvested portion of service-based restricted stock granted from 2008 until 2010 to officers and other employees that is contingently redeemable in cash upon a change in control (in dollars)	17.2	18.6
Restricted Stock Awards \| Minimum
Stock Based Compensation
Period of sales restrictions on restricted stock	10
Restricted Stock Awards \| Maximum
Stock Based Compensation
Period of sales restrictions on restricted stock	5
Performance-Based Units
Stock Based Compensation
Compensation expense (benefit) related to stock-based awards	14.7	6.2	1.5
Performance-based unit awards vested, amount paid	1.3
Summarized share information for restricted stock awards
Unrecognized compensation cost related to the unvested portion of outstanding stock-based awards (in dollars)	11.7
Period over which unrecognized compensation is expected to be recognized (in months)	26
Per unit value of Performance-Based Units (in dollars per unit)	$ 1
Service and performance period (in years)	3 years
Equity-Based Grants
Summarized share information for restricted stock awards
Compensation expense related to equity-based grants to members of the Board of Directors	$ 1.1	$ 0.8	$ 0.9

Represents period of restriction on sale of restricted stock.

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Represents the amount paid by the entity upon vesting of performance-based unit awards.

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This element represents the per unit value of performance-based units for which the fair value of the award is remeasured at each reporting period.

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This element represents the unvested portion of service-based restricted stock granted from 2007 until 2009 to officers and other employees that is contingently redeemable in cash upon a change in control.

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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.

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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.

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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.

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

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Description of the period of time over which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, which may be expressed in a variety of ways (for example, in years, month and year).

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The maximum vesting term over which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition.

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The minimum vesting term over which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition.

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No definition available.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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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).

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The weighted average fair value at grant date for nonvested equity-based awards issued 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).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The total fair value of equity-based awards for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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The amount of expense reported during the period resulting from the transaction in which equity securities were issued to pay for goods or nonemployee services.

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