REVENUE: - Revenue by Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenue Recognition
Net sales	$ 2,680.9	$ 2,129.1	$ 8,110.4	$ 5,634.2
Corporate, other and eliminations
Revenue Recognition
Net sales	(42.8)	(29.7)	(107.9)	(78.0)
Mexican Open-pit | Operating segment
Revenue Recognition
Net sales	1,425.8	1,181.7	4,536.6	3,152.1
Mexican IMMSA Unit | Operating segment
Revenue Recognition
Net sales	175.1	140.9	460.8	377.0
Peruvian Operations | Operating segment
Revenue Recognition
Net sales	1,122.8	836.2	3,220.9	2,183.1
Copper
Revenue Recognition
Net sales	2,110.4	1,749.9	6,576.1	4,585.4
Copper | Corporate, other and eliminations
Revenue Recognition
Net sales	(21.8)	(14.1)	(54.7)	(34.7)
Copper | Mexican Open-pit | Operating segment
Revenue Recognition
Net sales	1,195.0	1,022.1	3,858.2	2,687.8
Copper | Mexican IMMSA Unit | Operating segment
Revenue Recognition
Net sales	24.3	21.2	75.5	50.9
Copper | Peruvian Operations | Operating segment
Revenue Recognition
Net sales	912.9	720.7	2,697.1	1,881.4
Molybdenum
Revenue Recognition
Net sales	294.5	119.8	746.3	352.8
Molybdenum | Mexican Open-pit | Operating segment
Revenue Recognition
Net sales	146.6	58.2	387.3	188.3
Molybdenum | Peruvian Operations | Operating segment
Revenue Recognition
Net sales	147.9	61.6	359.0	164.5
Silver
Revenue Recognition
Net sales	104.2	133.0	363.4	320.4
Silver | Corporate, other and eliminations
Revenue Recognition
Net sales	(19.0)	(17.5)	(48.1)	(38.9)
Silver | Mexican Open-pit | Operating segment
Revenue Recognition
Net sales	52.4	67.0	193.1	170.6
Silver | Mexican IMMSA Unit | Operating segment
Revenue Recognition
Net sales	37.2	48.4	122.6	111.1
Silver | Peruvian Operations | Operating segment
Revenue Recognition
Net sales	33.6	35.1	95.8	77.6
Zinc
Revenue Recognition
Net sales	98.7	62.2	215.6	175.4
Zinc | Corporate, other and eliminations
Revenue Recognition
Net sales	0.1	4.6	0.5	1.3
Zinc | Mexican IMMSA Unit | Operating segment
Revenue Recognition
Net sales	98.6	57.6	215.1	174.1
Other
Revenue Recognition
Net sales	73.1	64.2	209.0	200.2
Other | Corporate, other and eliminations
Revenue Recognition
Net sales	(2.1)	(2.7)	(5.6)	(5.7)
Other | Mexican Open-pit | Operating segment
Revenue Recognition
Net sales	31.8	34.4	98.0	105.4
Other | Mexican IMMSA Unit | Operating segment
Revenue Recognition
Net sales	15.0	13.7	47.6	40.9
Other | Peruvian Operations | Operating segment
Revenue Recognition
Net sales	$ 28.4	$ 18.8	$ 69.0	$ 59.6