9. Share-based Compensation Restricted Stock (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost from restricted stock	$ 0.5
Nonvested shares - Weighted Average Grant Date Fair Value	$ 84.07	$ 83.21	$ 82.86	$ 88.09
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Outstanding beginning of period	39,629	68,893	101,247
Restricted Stock Units - Vested	(25,124)	(26,179)	(28,518)
Restricted Stock Units - Forfeited	(1,548)	(3,085)	(3,836)
Outstanding end of period	12,957	39,629	68,893
Restricted Stock Units Vested - Weighted-Average Grant-Date Fair Value	$ 81.98	$ 81.98	$ 81.94
Resticted Stock Units Cancelled/forfeited - Weighted-Average Grant-Date Fair Value	$ 84.20	$ 82.63	$ 83.47
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	1 year
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost from restricted stock	$ 26.6
Nonvested shares - Weighted Average Grant Date Fair Value	$ 88.31	$ 80.61	$ 77.01	$ 96.45
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Outstanding beginning of period	299,362	242,222	163,198
Restricted Stock Units Granted	138,840	127,920	126,330
Restricted Stock Units - Vested	(75,466)	(54,350)	(33,825)
Restricted Stock Units - Forfeited	(14,235)	(16,430)	(13,481)
Outstanding end of period	348,501	299,362	242,222
Weighted Average Grant Date Fair Value - Granted	$ 107.32	$ 98.25	$ 84.57
Restricted Stock Units Vested - Weighted-Average Grant-Date Fair Value	$ 85.52	$ 79.67	$ 78.41
Resticted Stock Units Cancelled/forfeited - Weighted-Average Grant-Date Fair Value	$ 89.31	$ 80.70	$ 79.71
Weighted Average Remaining Contractual Term (in years)	2 years 2 months 1 day
Resticted Stock Units Outstanding Aggregate Intrinsic Value (in millions)	$ 36.6
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	4 years

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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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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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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- Definition

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).

+ References

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The intrinsic value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit 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 or units, as calculated by applying the disclosed pricing methodology.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit 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 or units.

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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

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

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan 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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- 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.

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