Related party transactions (Details) - CNY (¥) ¥ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Beijing Dasheng Zhixing Technology Co., Ltd
Related party transactions
Fair value of promotion	¥ 76	¥ 535

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.

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