FAIR VALUE MEASUREMENT - Significant unobservable inputs (Details)	12 Months Ended
Dec. 31, 2017
Significant unobservable inputs used in the valuation
Dividend yield (as a percent)	0.00%
Minimum
Significant unobservable inputs used in the valuation
Weighted average cost of capital (as a percent)	14.50%
Lack of marketability discount (as a percent)	10.00%
Risk-free rate (as a percent)	1.80%
Expected volatility (as a percent)	32.94%
Maximum
Significant unobservable inputs used in the valuation
Weighted average cost of capital (as a percent)	17.00%
Lack of marketability discount (as a percent)	15.00%
Risk-free rate (as a percent)	3.50%
Expected volatility (as a percent)	38.00%
Liquidation scenario \| Minimum
Significant unobservable inputs used in the valuation
Probability (as a percent)	20.00%
Liquidation scenario \| Maximum
Significant unobservable inputs used in the valuation
Probability (as a percent)	70.00%
Redemption scenario \| Minimum
Significant unobservable inputs used in the valuation
Probability (as a percent)	20.00%
Redemption scenario \| Maximum
Significant unobservable inputs used in the valuation
Probability (as a percent)	30.00%
IPO scenario \| Minimum
Significant unobservable inputs used in the valuation
Probability (as a percent)	30.00%
IPO scenario \| Maximum
Significant unobservable inputs used in the valuation
Probability (as a percent)	60.00%

Represents the probability rate, used as an input to measure fair value.

No definition available.

Name:	ctrp_FairValueInputsProbabilityRate
Namespace Prefix:	ctrp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Expected dividends to be paid to holders of the underlying shares or financial instruments (expressed as a percentage of the share or instrument's price).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueAssumptionsExpectedDividendRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Measure of dispersion, in percentage terms (for instance, the standard deviation or variance), for a given stock price.

+ References

+ Details

Name:	us-gaap_FairValueAssumptionsExpectedVolatilityRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Risk-free interest rate assumption used in valuing an instrument.

+ References

+ Details

Name:	us-gaap_FairValueAssumptionsRiskFreeInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- 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.

+ Details

Name:	us-gaap_FairValueInputsAssetsQuantitativeInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Adjustment to the discount rate used to measure fair value for lack of ability to convert business interests into cash quickly.

+ References

+ Details

Name:	us-gaap_FairValueInputsDiscountForLackOfMarketability
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

+ Details

Name:	us-gaap_FairValueInputsDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ctrp_ProbabilityByScenarioAxis=ctrp_LiquidationScenarioMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ctrp_ProbabilityByScenarioAxis=ctrp_RedemptionScenarioMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ctrp_ProbabilityByScenarioAxis=ctrp_IPOScenarioMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: