ACQUISITIONS - Khoemacau (Details) - Khoemacau oz in Millions, $ in Millions	Feb. 25, 2019 USD ($) oz	Mar. 31, 2019 USD ($)
Acquisitions
Maximum contribution amount	$ 212	$ 212
Silver production acquired (as a percent)	80.00%
Option contribution amount	$ 53
Silver production option (as a percent)	20.00%
Rate reduction (as a percent)	50.00%
Silver production after threshold (as a percent)	40.00%
Rate reduction threshold | oz	32
Rate reduction threshold with option | oz	40
Spot price paid (as a percent)	20.00%
Increased level of throughput (as a percent)	30.00%
Cupric required initial investment	$ 100
Contributions payable in 2019	60
Contributions payable in 2020	125
Loan receivable commitment	$ 25
Loan receivable term	7 years
LIBOR
Acquisitions
Loans receivable variable interest rate (as a percent)	11.00%