XML 389 R186.htm IDEA: XBRL DOCUMENT v3.10.0.1
Financial instruments and risk management - Summary of financial assets by categories (Parenthetical) (Detail) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Disclosure Of Financial Assets [Abstract]    
Highly liquid financial assets held in managed investment funds classified as held for trading $ 2,522 $ 958