INVESTMENTS IN ASSOCIATES - SUMMARISED BALANCE SHEETS (Details) ¥ in Thousands, $ in Thousands	Dec. 31, 2020 CNY (¥)	Dec. 31, 2020 USD ($)	[1]	Dec. 31, 2019 CNY (¥)	Dec. 31, 2018 CNY (¥)	Dec. 31, 2017 CNY (¥)
Disclosure of associates [line items]
Current assets	¥ 6,258,837	$ 959,209		¥ 6,703,937
Non-current assets	30,521,616	4,677,641		30,189,196
Total assets	36,780,453	5,636,850		36,893,133
Current liabilities	7,144,739	1,094,976		6,477,044
Equity	28,156,169	$ 4,315,123		29,139,281	¥ 28,816,329	¥ 28,607,408
Share of net assets	196,848			174,686
Guangzhou Tiecheng Enterprise Company Limited (Tiecheng) [member]
Disclosure of associates [line items]
Current assets	93,571			77,732
Non-current assets	373,860			361,864
Total assets	467,431			439,596
Current liabilities	221,928			223,295
Equity	245,503			216,301	239,651
Share of net assets	120,296			105,987
Carrying amount of interest in associates	120,296			105,987	117,429
Shenzhen Guangzhou Railway Civil Engineering Company (Shentu) [member]
Disclosure of associates [line items]
Current assets	1,974,930			1,612,909
Non-current assets	10,209			12,941
Total assets	1,985,139			1,625,850
Current liabilities	1,828,909			1,485,647
Equity	156,230			140,203
Share of net assets	76,552			68,699
Carrying amount of interest in associates	¥ 76,552			¥ 68,699	¥ 64,296

[1] Translation of amounts from Renminbi ("RMB") into United States dollars ("US$") for the convenience of the reader has been made at US$1.00=RMB6.5250, the certified exchange rates for December 31, 2020 as published by the Federal Reserve Board of the United States. No representation is made that the RMB amounts could have been, or could be, converted into US$ at that rate on December 31, 2020 or on any other date.