XML 244 R219.htm IDEA: XBRL DOCUMENT v3.21.1
Exploration in operating units - Additional information (Details) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Exploration in operating units      
Disbursement of exploration in operating activities $ 28.0 $ 44.2 $ 89.7