XML 267 R253.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2
Post-retirement benefits - Summary of main assumptions rate for valuations of plans (Parenthetical) (Detail)
Dec. 31, 2019
Dec. 31, 2018
Disclosure of information about defined benefit plans [abstract]    
Assumption for the consumer price index 2.00% 2.20%