Stock-Based Compensation Long-Term Performance Restricted Stock Unit Award Monte Carlo Pricing Model Assumptions (Details) - Restricted Stock Units (RSUs) [Member] - $ / shares	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, weighted average grant date fair value (in dollars per share)		$ 65.22	$ 65.54
Long Term Performance Restricted Stock Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	27.90%	28.00%	28.00%
Risk-free interest rate	1.40%	2.20%	1.00%
Expected term (years)	2 years 3 months 18 days	2 years 1 month 6 days	1 year 8 months 12 days
Granted, weighted average grant date fair value (in dollars per share)	$ 80.64	$ 78.56	$ 77.75

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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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

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.

+ References

No definition available.

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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