The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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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.

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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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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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No definition available.

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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.

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- Definition

Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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- Definition

Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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PRINCIPAL ACCOUNTING POLICIES - Share-Based Compensation (Details)	12 Months Ended
	Dec. 31, 2019 $ / shares	Dec. 31, 2019 ¥ / shares	Dec. 31, 2018 $ / shares	Dec. 31, 2018 ¥ / shares	Dec. 31, 2017 $ / shares	Dec. 31, 2017 ¥ / shares	Dec. 31, 2016 ¥ / shares
Share based compensation
Weighted average fair value per stock option on grant date (in dollars or CNY per share) \| (per share)	$ 22.12	¥ 153.95	$ 21.53	¥ 148.05	$ 15.62	¥ 101.63	¥ 101.63
Risk-free interest rate (as a percent)					1.61%	1.61%
Expected life (years)	4 years	4 years	4 years	4 years	4 years	4 years
Expected dividend yield (as a percent)	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%
Volatility (as a percent)			32.00%	32.00%	32.00%	32.00%
Weighted average fair value of the common share on date of option grant	$ 69.46		$ 73.46		$ 56.68
Minimum
Share based compensation
Risk-free interest rate (as a percent)	1.61%	1.61%	2.41%	2.41%
Volatility (as a percent)	35.00%	35.00%
Maximum
Share based compensation
Risk-free interest rate (as a percent)	2.47%	2.47%	2.75%	2.75%
Volatility (as a percent)	38.00%	38.00%