Employee benefit plans and stock-based compensation plans (reflecting the two-for-one stock split (Details Textuals) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2010 Year Day Subsidiary	Dec. 31, 2009	Dec. 31, 2008
Employee benefit plans and stock-based compensation plans (Textuals)
Retirement Savings Plan employees contribution as a percentage of salary	15% to 25%
Employers contribution as a percentage on first one percent on employees contribution	200.00%
Employers contribution as a percentage on next three percent on employees contribution	100.00%
Retirement savings plan, contribution expense	$ 26.8	$ 22.0	$ 19.7
Employees contribution to Employees Stock purchase plan as a percentage of Employees salary	10.00%
Employee Stock Purchase plan Purchase price of shares as a percentage on fair market value	95.00%
Common stock issued under employee stock purchase plan	217,000	260,000	236,000
Common stock reserved for future purchases under the employee stock purchase plan	2,600,000
Contribution by employee for deferred compensation plan's benefit payments from base earnings percentage	50.00%
Contribution by employee for deferred compensation plan's benefit payments from specific bonus percentage	100.00%
Deferred Compensation Plan Employer Contribution As Percentage On Employees Contribution	6.00%
Employers Contribution allocated to Hypothetical Investment In Common Stock Percentage	25.00%
Net deferred compensation plan expense	1.5	(0.6)	1.8
Reserved common stock under deferred compensation plan	5,900,000
Common stock available for issuance under stock-based compensation plans	14,200,000
Maximum contractual term of stock options and SSRs, restricted stock and performance shares, year	10
Restricted stock units and performance shares granted	300,000
Weighted average fair market value of restricted stock units and performance shares	$ 49.59
Performance shares granted to certain officers exceeding certain performance measures	213,000
Maximum multiplier used to calculate value of performance shares	2.5
Total number of non-vested restricted stock and performance share awards	1,000,000	1,200,000
Stock options granted	2,500,000
Weighted average fair value of options granted during the year	$ 15.97	$ 7.27	$ 8.94
Stock options and stock settled appreciation rights vesting grade	3
Vesting period of stock option plan	3
Unearned compensation related to unvested shares for deferred compensation plan	0.3	0.3
Windfall tax benefit related to stock options exercised	58.9
Tax benefit related to employee stock compensation	18.1	16.6	14.3
Weighted average remaining recognition period for SSRs and stock options	1.4
Weighted average remaining recognition period for restricted stock and performance shares	1.4
Weighted average remaining contractual term of stock options and stock settled appreciation rights outstanding	4.2
Weighted average remaining contractual term of stock options and stock settled appreciation rights exercisable	3.1
Intrinsic value shares outstanding	348.6
Intrinsic value shares exercisable	229.5
Restricted Stock and Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax compensation expense	17.5	16.2	16.3
Unearned compensation expense	16.5	16.7
Employee benefit plans and stock-based compensation plans (Textuals)
Unearned compensation expense	16.5	16.7
SSRs And Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax compensation expense	32.1	28.6	23.8
Unearned compensation expense	23.9	21.7
Employee benefit plans and stock-based compensation plans (Textuals)
Unearned compensation expense	$ 23.9	$ 21.7

Contribution by employee for deferred compensation plan's benefit payments from base earnings percentage.

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Contribution by employee for deferred compensation plan's benefit payments from specific bonus percentage.

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Deferred compensation plan common stock reserved for issuance.

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Deferred Compensation Plan Employer Contribution as a percentage on employees contribution.

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Employees contribution to Employees Stock purchase plan as a percentage of Employees salary.

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Employee Stock Purchase plan Purchase price of shares as a percentage on fair market value.

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Employers Contribution allocated to Hypothetical Investment In Common Stock Percentage.

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Employers contribution as a percentage on first one percent on employees contribution.

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Employers contribution as a percentage on next three percent on employees contribution.

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Maximum multiplier used to calculate value of performance shares.

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Performance shares granted to certain officers exceeding certain performance measures.

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Retirement Savings Plan employees contribution as a percentage of salary.

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Maximum contractual term of stock options and SSRs, restricted stock and performance shares, year.

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Share based compensation arrangement by share based payment award stock options and stock settled appreciation rights vesting grade.

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Share Based Compensation Arrangement By Share Purchase Plan Number Of Shares Reserved For Issuance.

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Stock-based compensation plans.

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Tax benefit related to employee stock compensation.

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Unearned compensation related to unvested shares for deferred compensation plan.

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Weighted Average Remaining Contractual Term Of Stock Options And Stock Settled Appreciation Rights Exercisable.

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Weighted Average Remaining Contractual Term Of Stock Options And Stock Settled Appreciation Rights Outstanding.

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Weighted average remaining recognition period for restricted stock and performance shares.

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Weighted average remaining recognition period for SSRs and stock options.

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

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 64

-Subparagraph b

Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-Paragraph A240

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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F

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The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 64, 65

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-Publisher AICPA

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-Number 12

-Paragraph 6, 7

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The amount of contributions made by the employer.

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

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Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual 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 number of shares issuable under a share-based award plan pertaining to grants made during the period on other than stock option plans (for example, phantom stock plan, stock appreciation rights plan, performance target plan).

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-Subparagraph b(2)(c)

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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).

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The number of outstanding awards on nonstock 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.

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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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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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The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of vested portions of options outstanding and currently exercisable under the option plan as of the balance-sheet date.

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

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-Name Statement of Financial Accounting Standard (FAS)

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-Subparagraph b(1)(d)

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-Subparagraph c(1)

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The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices pertaining to options outstanding under the plan as of the balance-sheet date.

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-Publisher FASB

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-Number 123R

-Paragraph A240

-Subparagraph d(1)

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Number of shares issued during the period as a result of an employee stock purchase plan.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Principles Board Opinion (APB)

-Number 12

-Paragraph 10

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 5

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