SUMMARY OF PRINCIPAL ACCOUNTING POLICIES - Impairment of long-lived assets (Details) - CNY (¥) ¥ in Millions	6 Months Ended
Jun. 30, 2025	Jun. 30, 2024
SUMMARY OF PRINCIPAL ACCOUNTING POLICIES
Long-lived asset impairment loss	¥ 38	¥ 36
Impairment Long Lived Asset Held For Use Statement Of Income Or Comprehensive Income Extensible Enumeration Not Disclosed Flag	true

The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

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Reference 2: http://www.xbrl.org/2003/role/exampleRef
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Period Type:	duration