Share-Based Compensation (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Share-Based Compensation
Number of share-based compensation plans	1		1
Compensation cost recognized for share-based awards	$ 4,800,000	$ 4,200,000	$ 9,500,000	$ 8,100,000
Cash received from the exercise of stock options			4,507,000	17,761,000
Tax benefit recognized for share-based compensation arrangements			1,000,000	2,200,000
Share-based compensation
Shares available for future grants (in shares)	1.4		1.4
Share-based compensation, fair value
Volatility look back period (in years)			20
Stock options
Share-based compensation
Vesting period (in years)			4Y
Expiration period (in years)			10 years
Share-based compensation, fair value
Weighted-average volatility (as a percent)	30.85%	31.38%	30.91%	31.41%
Dividend yield (as a percent)	2.48%	0.69%	1.47%	0.73%
Expected term (in years)	5.81	5.80	6.04	6.08
Risk-free interest rate (as a percent)	2.24%	2.83%	2.97%	2.99%
Weighted-average grant-date fair values of options granted (in dollars per share)			$ 18.38	$ 16.86
Total intrinsic values of options exercised			$ 2,500,000	$ 9,000,000
Restricted stock
Share-based compensation
Vesting period (in years)			at least three years
Vesting Period for awards issued under predecessor plans (in years)			5

Represents the vesting period of the share-based compensation awards issued under the predecessor plans.

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- Definition

The period over which the volatility is observed to estimate the volatility factor to be used in Black-Scholes valuation model.

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- Definition

The number of share-based compensation plans approved by the entity's shareholders.

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- Definition

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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- 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

The cash inflow associated with the amount received from holders exercising their stock options. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately.

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- Definition

The date when the equity-based award expires as specified in the award agreement, which may be presented in a variety of ways (for example, year, month and year, day, month and year, quarter of a year).

+ References

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- Definition

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).

+ References

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The period of time an equity-based award is expected to be outstanding. An equity-based award's expected term is generally determined based on, among other factors, the instrument's contractual term and the effects of employees' expected exercise and post-vesting employment termination behavior.

+ References

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

+ References

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- Definition

The range of expected volatilities used and the weighted-average expected volatility for an entity using a valuation technique with different volatilities during the contractual term.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- Definition

The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

+ References

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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