9. Share-based Compensation Restricted Stock (Details) (Restricted Stock Units (RSUs) [Member], USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value	$ 10.6	$ 9.6	$ 8.5
Total unrecognized compensation cost from restricted stock	$ 33.9
Nonvested shares - Weighted Average Grant Date Fair Value	$ 105.44	$ 96.15	$ 87.81	$ 112.60
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Outstanding beginning of period	375,430	361,458	338,991
Restricted Stock Units Granted	145,695	144,445	138,840
Restricted Stock Units - Vested	(107,557)	(104,883)	(100,590)
Restricted Stock Units - Forfeited	(36,203)	(25,590)	(15,783)
Outstanding end of period	377,365	375,430	361,458
Weighted Average Grant Date Fair Value - Granted	$ 119.56	$ 117.09	$ 107.32
Restricted Stock Units Vested - Weighted-Average Grant-Date Fair Value	$ 98.52	$ 91.76	$ 84.64
Resticted Stock Units Cancelled/forfeited - Weighted-Average Grant-Date Fair Value	$ 108.17	$ 95.97	$ 88.81
Weighted Average Remaining Contractual Term (in years)	3 years 6 months 15 days
Resticted Stock Units Outstanding Aggregate Intrinsic Value (in millions)	$ 45.5
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	4 years

Unrecognized cost of unvested share-based compensation awards.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

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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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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).

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Per share weighted average intrinsic value of equity-based compensation awards not vested. Excludes stock and unit options.

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

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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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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Number of options outstanding, including both vested and non-vested options.

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