Stock-Based Compensation (Summary of Activity in Corporation's Active Stock Plans) (Details) (USD $)	6 Months Ended
Jun. 30, 2011
Beginning Balance, Shares Available for Grant	2,759,347
Beginning Balance, Director Deferred Stock Units Outstanding	16,515
Granted, Shares Available for Grant	(5,577)
Granted, Director Deferred Stock Units Outstanding	5,577
Granted, Number of Shares
Stock options exercised, Shares Available for Grant
Stock options exercised, Director Deferred Stock Units Outstanding
Stock awards vested, Shares Available for Grant
Stock awards vested, Director Deferred Stock Units Outstanding
Forfeited, Shares Available for Grant	41,625
Forfeited, Director Deferred Stock Units Outstanding
Ending Balance, Shares Available for Grant	2,795,395
Ending Balance, Director Deferred Stock Units Outstanding	22,092
Stock Options Outstanding [Member]
Beginning Balance, Number of Shares	4,383,885
Beginning Balance, Weighted-Average Exercise Price	$ 52.08
Granted, Number of Shares
Granted, Weighted-Average Exercise Price
Stock options exercised, Shares Available for Grant
Stock options exercised, Number of Shares	(144,203)
Stock options exercised, Weighted-Average Exercise Price	$ 50.19
Stock awards vested, Number of Shares
Stock awards vested, Weighted-Average Exercise Price
Forfeited, Number of Shares	(41,625)
Forfeited, Weighted-Average Exercise Price	$ 51.45
Ending Balance, Number of Shares	4,198,057
Ending Balance, Weighted-Average Exercise Price	$ 52.15
Non-Vested Stock Awards Outstanding [Member]
Beginning Balance, Number of Shares	227,550
Beginning Balance, Weighted-Average Grant-Date Fair Value	$ 51.10
Granted, Number of Shares
Granted, Weighted-Average Grant-Date Fair Value
Stock options exercised, Shares Available for Grant
Stock options exercised, Number of Shares
Stock options exercised, Weighted-Average Grant-Date Fair Value
Stock awards vested, Number of Shares	(85,420)
Stock awards vested, Weighted-Average Grant-Date Fair Value	$ 50.64
Forfeited, Number of Shares
Forfeited, Weighted-Average Grant-Date Fair Value
Ending Balance, Number of Shares	142,130
Ending Balance, Weighted-Average Grant-Date Fair Value	$ 51.38

Schedule of Recognized Stock Based Compensation Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures Deferred Stock Units Outstanding

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Share Based Compensation Arrangement By Share Based Payment Award Options Deferred Stock Units Outstanding

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Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Deferred Stock Units Outstanding Grants In Period

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Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Weighted Average Grant Date Fair Value

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Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures Shares Available for Grant

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Share Based Compensation Arrangement By Share Based Payment Award Options Number Of Shares Available for Grant, Granted

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Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Exercisable Deferred Stock Units Outstanding

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Exercisable Shares Available for Grant

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Share Based Compensation Arrangement By Share Based Payments Award Grant Deferred Stock Units Outstanding

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- Definition

The weighted average fair value as of the grant date of share-based award plans other than stock option plans that were not exercised or put into effect during the reporting period as a result of the occurrence of a terminating event specified in the contractual agreement of the plan.

+ References

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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph b(2)(e)

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- Definition

The weighted average fair value at grant for nonvested share-based awards issued during the period on other than stock option plans (for example, phantom stock plan, stock appreciation rights plan, performance target plan).

+ References

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-Number 123R
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-Subparagraph b(2)(c)

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-Paragraph A240
-Subparagraph c(1)

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- Definition

The weighted average fair value of nonvested awards on share-based plans excluding option plans (for example, phantom stock plan, stock appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares.

+ References

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-Number 123R
-Paragraph A240
-Subparagraph b(2)(a)

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-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
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- Definition

The weighted average fair value as of grant dates pertaining to a share-based award plan other than a stock option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares, other instruments, or cash in accordance with the terms of the arrangement.

+ References

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-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph b(2)(d)

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- Definition

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

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- Definition

The number of shares into which fully or partially vested stock options outstanding as of the balance-sheet date can be currently converted under the option 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(1)(c), d(2)

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- Definition

The weighted average price at which option holders acquired shares when converting their stock options into shares under the plan during the reporting period.

+ References

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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph b(1)(e)

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- Definition

The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

+ References

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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph b(1)(f)

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- Definition

The weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated during the reporting period due to noncompliance with plan terms during the reporting period.

+ References

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-Subparagraph b(1)(f)

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- Definition

The quantity of shares issuable on stock options awarded under the plan during the reporting period.

+ References

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-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
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- Definition

The weighted average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on stock options awarded under the plan during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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- Definition

The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance-sheet date, including vested options.

+ References

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-Publisher FASB
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-Number 123R
-Paragraph A240
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- Definition

The weighted average price as of the beginning of the year at which grantees can acquire the shares reserved for issuance under the stock option plan.

+ References

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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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- Definition

As of the balance sheet date, the number of shares for which fully vested and expected to vest stock options can be exercised under the option plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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-Subparagraph d(2)

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- Definition

As of the balance sheet date, the weighted-average exercise price for outstanding stock options that are fully vested or expected to vest.

+ References

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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph d(1)

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