Employee benefit plans and stock-based compensation plans (reflecting the two-for-one stock split (Details 3) (USD $) In Millions, except Per Share data	12 Months Ended
Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Total stock options exercised and restricted shares vested
Proceeds from stock options exercised	$ 38.2	$ 9.4	$ 27.7
Fair value of vested restricted shares	10.5	12.4	4.3
Intrinsic value of stock options exercised	$ 123.7	$ 48.8	$ 41.7
Weighted average fair value of options granted during the year	$ 15.97	$ 7.27	$ 8.94

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Aggregate proceeds received by the entity during the annual period from exercises of stock options and conversion of similar instruments granted under share-based payment arrangements.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph i

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- Definition

The total fair value of share-based awards 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

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph c(2)

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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

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph c(2)

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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.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph c(1)

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