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Fair Value Measurements - Additional Information (Detail)
¥ in Millions, $ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2018
USD ($)
Sep. 30, 2018
CNY (¥)
Sep. 30, 2017
CNY (¥)
Sep. 30, 2018
USD ($)
Sep. 30, 2018
CNY (¥)
Sep. 30, 2017
CNY (¥)
Disclosure Reconciliation Of Changes In Fair Value [Abstract]            
Long-term investments impartment charges $ 45 ¥ 298 ¥ 197 $ 58 ¥ 396 ¥ 197