PRINCIPAL ACCOUNTING POLICIES - LEASEHOLD LAND PAYMENTS (Details)	12 Months Ended
	Dec. 31, 2017
Disclosure of maturity analysis of operating lease payments [line items]
Lease terms	20 years
Minimum [member]
Disclosure of maturity analysis of operating lease payments [line items]
Lease terms	36 years 6 months
Maximum [member]
Disclosure of maturity analysis of operating lease payments [line items]
Lease terms	50 years