REVENUE: - Receivables by reporting segment (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021 USD ($) T	Dec. 31, 2020 USD ($)
Opening and closing balances of receivables
Trade receivables	$ 1,493.4	$ 1,068.9
Related parties, current	34.6	23.3
Corporate, other and eliminations
Opening and closing balances of receivables
Related parties, current	$ 7.8	7.1
Copper concentrates
Long Term Contracts
Long term contracts | T	188,000
Copper cathodes
Long Term Contracts
Long term contracts | T	48,000
Molybdenum concentrates
Long Term Contracts
Long term contracts | T	41,414
Sulfuric acid
Long Term Contracts
Long term contracts | T	322,415
Mexican Open-pit | Operating segment
Opening and closing balances of receivables
Trade receivables	$ 658.8	566.0
Related parties, current	25.1	15.4
Mexican IMMSA Unit | Operating segment
Opening and closing balances of receivables
Trade receivables	57.1	57.8
Peruvian Operations | Operating segment
Opening and closing balances of receivables
Trade receivables	777.5	445.1
Related parties, current	$ 1.7	$ 0.8