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GOODWILL - KEY ASSUMPTIONS USED FOR VALUE-IN-USE CALCULATIONS (Details) - CNY (¥)
¥ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Disclosure of goodwill key assumptions used for value-in-use calculation [line items]    
Period over which calculations use pre-tax cash flow projections based on financial forecasts prepared by management P5Y  
Amount by which unit's recoverable amount exceeds its carrying amount ¥ 4,997 ¥ 5,515
Railroad Businesses [member]    
Disclosure of goodwill key assumptions used for value-in-use calculation [line items]    
Gross margin (beyond the five-years period) 16.30% 16.73%
Growth rate (beyond the five-years period) 2.00% 2.00%
Discount rate 12.44% 12.44%